Carburetor
Models 4MV-4MC-M4ME-M4M C
Service Manual
:A A L
Delco
9D- 5
March 198 1
Supersedes 9D-5
Dated May 197 3
IMPORTANT SAFETY NOTIC E
Proper service and repair is important to the safe, reliable operation of all motor vehicles .
The procedures recommended by Rochester Products Division of General Motors an d
described in this service manual are effective methods of performing service operations .
Some of these service operations require the use of tools specially designed for the purpose .
The special tools should be used when and as recommended .
It is important to note that this manual contains various CAUTIONS and NOTICES whic h
should be carefully read in order to minimize the risk of personal injury to service personne l
or the possibility that improper service methods will be followed which may damage th e
vehicle or render it unsafe . It is also important to understand that these Cautions an d
Notices are not exhaustive . Rochester Products could not possibly know, evaluate an d
advise the service trade of all conceivable ways in which service might be done or of th e
possible hazardous consequences of each way . Consequently, Rochester Products has no t
undertaken any such broad evaluation . Accordingly, anyone who uses a service procedur e
or tool which is not recommended by Rochester Products must first satisfy himsel f
thoroughly that neither his safety nor vehicle safety will be jeopardized by the servic e
method he selects .
All information, illustrations, and specifications contained in this manual are based on th e
latest product information available at time of publication approval . The right is reserved t o
make changes at any time without notice .
CONTENTS
GENERAL DESCRIPTION
3
OPERATING SYSTEMS
4
MAJOR SERVICE OPERATIONS 26
NOTE : USE THIS MANUAL PLUS SECTIONS 9D-5A & 9D-5S FOR COMPLETE SERVIC E
INSTRUCTIONS .
©1981 GENERAL MOTORS CORPORATIO N
PRINTED IN U .S.A.
J
9D- 5
March 198 1
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TYPICAL MODELS-4MV-M4M E
Figure 1 Model 4MV
Figure 2 Model M4M E
GENERAL DESCRIPTIO N
The Rochester Quadrajet is a four barrel, two stag e
carburetor of down draft design . It has been proven to
be dependable and a versatile performer as witnessed by
its broad application and usage since its first introduction in 1965 . Modern demands for greater fuel econom y
and improved emission control have resulted in significant refinement of the original design . The Rochester
Quadrajet has evolved to the point of being an efficien t
and sophisticated fuel control device that is right fo r
the times and yet maintains the serviceability that is s o
important to those responsible for vehicle performanc e
and customer satisfaction .
The Quadrajet carburetor has two distinct and separate design stages . Each stage operates to provide a
blend of economical operation and responsive engin e
performance .
The primary side of the carburetor (fuel inlet side )
has two small bores . Each bore contains a triple venturi arrangement equipped with plain tube nozzles . Th e
triple venturi provides excellent fuel atomization an d
delivery in the off idle and part throttle ranges of engin e
operation .
Fuel metering is controlled through the usage of
tapered primary metering rods that are suspended withi n
finely machined metering jets . The metering rods are
moved vertically by engine vacuum control . This is accom plished by the use of a spring-loaded piston and ro d
hanger assembly and results in the control of fuel allowe d
to pass through the metering jets and to the engin e
during low speed and moderate speed operation .
Some models use multiple stage enrichment method s
that may incorporate additional rods, jets and/or powe r
piston arrangements . There are models that have device s
that respond to changes in atmospheric pressure as well .
The objective is to provide a high degree of sensitivit y
to air/fuel mixture control at lower and midrange engin e
speeds . The primary side of the Quadrajet carburetor
has the design features to meet these needs . The individual systems are described in detail later in sections o f
this text .
The secondary side of the Quadrajet has two larger
bores . This increased area, when combined with that o f
the primary side of the carburetor, provides an air de livery capacity that can satisfy a broad range of engin e
operating conditions .
An air valve, positioned above the secondary bores ,
controls the fuel delivery for high demand conditions .
This secondary air valve is connected mechanically to a
pair of secondary metering rods that are tapered and ar e
suspended within a pair of fuel metering orifices . Th e
fuel passing through these secondary orifices is directe d
to a set of delivery nozzles located at the top of each secon dary bore and below the air valve . The fuel flo w
through the nozzles is thereby controlled in direct pro portion to air flowing through the secondary bores .
There are two basic carburetor model designs :
First released in 1965, the 4MV is an automatic chok e
model designed for use with a manifold mounted thermostatic choke coil . The 4MC model also is an automatic
choke carburetor but with the choke thermostatic coi l
located in a choke housing mounted on the side of th e
float bowl . Except for choke systems, all models hav e
basically the same principles of operation (Figure 1) .
First released in 1975, the M4ME models differ fro m
the conventional 4MV-4MC carburetor models in tha t
the "M" prefix designates "modified", indicating th e
primary side is revised to accomodate an adjustabl e
metering rod assembly with filler spool, or aneroid metering rod assembly, where required, and the auxiliar y
power piston assembly (if used) . The aneroid feature is
normally used to achieve altitude compensation in air /
fuel mixtures (designated Models M4MCA-M4MEA )
(Figure 2) .
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March 198 1
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Later "modified " models use separated main well s
with an aneroid cavity insert in the float bowl replacing
the adjustable metering rod or aneroid-metering rod
assembly .
On all models, the fuel chamber is centrally locate d
to avoid problems of fuel spillage causing engine tur n
cut-out and delayed fuel flow to the carburetor bores .
The fuel chamber is relatively small in volume to reduc e
fuel evaporation during hot engine "shutdown" . A plastic
bowl insert is included to reduce the free volume abov e
the fuel level to prevent fuel loss to the main metering
jets during critical vehicle maneuvers .
The float system has a single pontoon float and fue l
inlet valve for simplification and ease of servicing . An
integral fuel filter (or strainer), and check valve (if used) ,
located in the float bowl ahead of the fuel inlet valve, is
easily removed for cleaning or replacement .
All models have an Adjustable Part Throttle (A .P .T . )
screw located either in the throttle body (since 1968 o n
4MV-4MC models) or in the float bowl ( " M" modifie d
models) to aid in refinement of fuel mixtures for goo d
emission control .
The thermostatic choke coil assembly on 4MV model s
is heated by hot exhaust gases that flow through a specia l
passage in the intake manifold . On 4MC-M4MC-an d
M4MCA models, the thermostatic coil assembly i s
warmed by exhaust heated air supplied through a tub e
to the choke housing mounted on the float bowl . M4ME
and M4MEA models use an electrically heated thermostatic coil assembly to control choke mixtures afte r
engine start and cold driveaway .
The throttle body is aluminum to reduce overall weigh t
and to improve heat distribution, plus there is a thick
throttle body to bowl insulator gasket to keep excessive
heat from the float bowl causing fuel percolation .
Some Quadrajet applications use a shim between th e
throttle body and flange gasket . The shim is used t o
protect the carburetor aluminum throttle body from exhaust gases flowing through the heat cross-over o r
exhaust gas recirculation passage in the intake manifold .
carburetors have no tag but include the part numbe r
stamped vertically on the left rear corner of the floa t
bowl casting adjacent to the secondary pick-up lever
(Figure 4) . If replacing the float bowl, follow the manufacturer ' s instructions contained in the service packag e
so that the identification number can be transferred t o
the new float bowl . Refer to the part number on th e
bowl when servicing the carburetor .
SHIF T
(DENT.
ASSEM .
PLANT COD E
MODEL NO .
YEAR
DAY OF YEAR
CARBURETOR IDENTIFICATIO N
"4M" TYPE
Figure 4 Carburetor Identification Location Late Model s
SERVICE FEATURE S
The primary side of the carburetor has six operatin g
systems . They are float, idle, main metering, power ,
pump, and choke . All systems receive fuel from one fue l
chamber .
The following text covers the operating systems fo r
ease in trouble-shooting and also recommended service
procedures . There are some design variations betwee n
different models which will be covered in that part of
the text pertaining to that particular system or service
procedure .
OPERATING SYSTEM S
CARBURETOR IDENTIFICATIO N
FLOAT SYSTE M
Early Quadrajet carburetors (Figure 3) have th e
model number identification stamped on a circular ta g
pressed into a recess on the float bowl casting in a fla t
area on the throttle lever side . Later model Quadraje t
The Quadrajet carburetor has a centrally located fue l
chamber in the float bowl (Figure 5) . The fuel chamber
is centered between the carburetor bores to assure a n
adequate fuel supply to all metering systems with respec t
to car inclination or severity of turns .
The float system (Figures 6 or 7) consists of a fuel
chamber, fuel filter (with check valve on M4MC-M4M E
applications) or a fuel inlet strainer (some 4MV applications), a single closed-cell plastic float pontoon wit h
integral float lever, a float hinge pin, float valve an d
pull-clip, float valve seat (with or without "windows " ) ,
and internal vents . Also, some applications include eithe r
an idle vent valve, vacuum vent switch valve, or externa l
CARBURETOR
MODEL N O
CHANGE
LETTER
CARBURETOR
A AT(
I5/
NOPEGOION
STAMP
MO B Y R
BUILT (JAN 1967 )
MODELS 0,2G .4G
MODELS M 4M
(EARLY)
Figure 3 Carburetor Identification Tag - Earl y
Models
9D• 5
March 198 1
Page 5
vent connector tube leading to the vapor canister, to
vent excessive fuel vapors that form in the fuel chambe r
above the fuel surface that could disrupt hot engin e
operation . A plastic filler block is located in the top o f
the fuel chamber over the float valve to prevent fue l
slosh in this area. On M4MC and M4ME models, either
a filler spool or an aneroid cavity insert is used in the
fuel chamber to reduce fuel slosh on turns . Also, a
metal baffle is added to the pump well fill slot in th e
float bowl of M4MC-M4ME models to reduce fuel slos h
during various vehicle maneuvers .
Figure 5 Centralized Fuel Chambe r
EXTERNA L
IDLE VEN T
VALV E
On most models, an integral 1-inch or 2-inch pleate d
paper fuel inlet filter, dependent upon model, is mounte d
in the front of the float bowl behind the fuel inlet nu t
to filter impurities from the incoming fuel . If used, a
check valve is pressed into the neck of the fuel filter .
The check valve consists of a plastic disc contained in a
plastic retainer. It is held in the normally closed positio n
by a small spring which exerts pressure on the check
valve . When the engine starts and fuel flow pressure fro m
the fuel pump enters the inlet nut, it pushes the smal l
check valve off its seat . Fuel flows past the valve int o
the inside of the filter and continues on through the filte r
to the float valve and seat . With the engine off, the
check valve closes and shuts off fuel flow to the carburetor to prevent fuel leaks if a vehicle roll-over should
occur .
The check valve retainer also has a flanged nec k
which seals between the filter and fuel inlet nut .
FUEL INLE T
FILTER
-J
NOTICE : If used, the check valve must b e
installed to meet government safety standard s
for roll-over . New service replacement filters
include the check valve where required .
The fuel filter is held in position by the force of a
spring located between the filter assembly and the fue l
inlet nut cavity .
.
Figure 6 Float System 4MV-4M C
NOTICE : It is very important that the filter
be serviced according to recommended maintenance intervals to prevent dirt and othe r
impurities from entering the carbureto r
metering orifices .
The float system operates in the following manner :
CHECK VALVE
SEAT
"'CHECK
VALVE
FLOAT SYSTEM
Figure 7 Float System M4MC-M4ME
Fuel flow from the fuel pump enters the carburetor
fuel inlet nut . It opens the check valve (if used) in th e
filter against spring force and flows through the filter
element (or strainer), and then passes from the filter
chamber up through the float valve seat and flows past
the float valve on into the fuel chamber . As the in coming fuel enters the fuel chamber, the float pontoo n
rises and forces the float valve closed, shutting off fuel
flow at a prescribed level . As fuel is used from the fue l
chamber, the float pontoon drops to open the float valve
allowing fuel to again enter the fuel chamber . This
cycle continues, maintaining a near constant fuel leve l
in the fuel chamber for all ranges of engine operation .
A float pull clip, fastened to the float valve, hook s
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over the edge of the float lever at the center as show n
in Figures 6 or 7 . Its purpose is to assist in lifting th e
float valve off its seat whenever fuel level in the fuel
chamber is low .
NOTICE: Do not place pull clip throug h
small holes in top of float lever . Severe flood ing will result .
There are two types of float valves used in the Quadra jet carburetor : One type is diaphragm assisted and th e
other is the conventional needle and brass seat .
The diaphragm assisted float valve (shown in the inset
Figure 6) is used primarily with a smaller float and o n
engines equipped with high pressure fuel pumps . The
valve seat is a brass insert and is pressed into the bow l
fuel inlet channel below the diaphragm needle tip . Th e
seat is not removable, as the valve tip is of a materia l
which makes seat wear negligible . Care should be use d
during servicing so that the seat is not nicked, scored ,
or moved . The float valve is factory staked and tested
and should not be re-staked in the field .
Fuel flow through the diaphragm assisted float valve
varies from the conventional float needle . With the conventional type (as shown in Figure 7) fuel flows fro m
the inlet filter and inlet channel up through the needl e
seat orifice past the float needle valve and spills ove r
into the float bowl . With the diaphragm type float valve ,
fuel from the inlet filter enters the channel above th e
float valve tip . When fuel level is low in the bowl, th e
float valve is off its seat and fuel flows down past th e
valve tip into a fuel channel which leads upward throug h
the bowl casting to a point above normal liquid leve l
and spills over into the float bowl .
The diaphragm type float valve differs in operatio n
from the conventional float needle in that a larger sea t
orifice can be used to provide greater fuel flow to the
float chamber and yet allow the use of a small float .
This is accomplished through a balance of forces actin g
on the float valve and diaphragm against fuel pum p
pressure . Fuel pressure entering the float valve chambe r
tends to force the valve closed . However, the same
pressure is also acting on the float valve diaphragm . The
diaphragm has a slightly larger area than the float
valve head, therefore the greater pressure acting on th e
diaphragm tends to push the valve off its seat . The
force of the float arm acting on the valve stem, as the
float bowl fills, overcomes this pressure difference and
closes the valve . Therefore, the floa t' s function is to overcome the pressure difference and it does not have t o
force a valve closed against direct fuel pump pressur e
as does the conventional needle type .
To improve hot engine starting and to prevent rough
idle which may'result from excessive fuel vapors tha t
may form in the fuel chamber, various methods have
been used to vent these vapors external to the carburetor .
Early Quadrajet applications vented these vapors t o
the atmosphere through an idle vent valve that is operated
mechanically . A wire tang on the pump lever open s
the valve during idle and allows the valve to close a t
greater throttle valve angles as in the off idle and par t
throttle positions .
Some models use a thermostatically controlled ven t
valve (Figure 8) . This heat sensitive valve is operated b y
a bi-metal strip which holds the valve closed at temperatures below 75°F . When temperatures at the carbureto r
exceed that value the valve opens allowing vapors t o
escape . The thermostatic vent valve is adjustable t o
make sure it is timed to open during idle and closed a t
higher engine speeds .
Figure 8 Thermostatic Idle Vent Valv e
VALV E
CONSTANT BLEED
RESTRICTIO N
VENT TO
CANISTER
VACUUM PASSAGE
VACUUM VENT VALVE
Figure 9 Bowl Vent Valve
Some Quadrajets have a vacuum operated vent valv e
(Figure 9) that is also controlled to function with a n
evaporative vapor canister . The vacuum vent valve i s
designed to be open and to allow fuel chamber vapor s
to be routed directly to a vapor collection canister instead of the atmosphere for improved evaporativ e
emission control during engine shut-down . A passage
beneath the vacuum diaphragm in the air horn pro -
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FIXED IDLE AIR
BY-PAS S
DLE CHANNE L
RESTRICTION
FUEL
BOWL VENT VALVE TO CANISTER
Figure 10 Bowl Vent Valv e
vides a constant purge of the vapors from the vapo r
canister during off idle and higher engine speeds .
Later "modified " versions of the Quadrajet have a
bowl vent valve that is spring-loaded and is actuate d
by action of a spacer on the pump plunger shaft (Figur e
10). The fuel chamber is externally vented to the vapo r
collection canister during periods of engine shut-down .
Another method used to vent vapors is by the additio n
of a tube to the air horn (see Figure 7) . Vapors flow
through this tube and connecting hose to a vacuu m
operated vapor vent valve that is an integral part of th e
vapor collection canister located elsewhere in the engin e
compartment . The canister vent valve is spring-loade d
and normally open, allowing bowl vapors to pass into th e
canister during engine shut down . Manifold vacuu m
during engine operation closes the valve and vapors ar e
purged from the canister . This system improves hot
engine starting and also meets government evaporativ e
emission requirements .
NOTICE : External venting of fuel chambe r
vapors is not 'used on Quadrajet carburetor s
designed for marine use .
IDLE SYSTE M
The Quadrajet carburetor idle system is located o n
the primary side (fuel inlet side) of the carburetor t o
supply the correct air/fuel mixture during idle and offidle operation .
The idle system is used during this period because
air flow through the carburetor venturi is not grea t
enough to obtain efficient metering from the main discharge nozzles . The idle system is only used in the tw o
primary bores of the carburetor . Each bore has a separat e
and independent idle circuit (Figure 11) .
The idle system consists of a calibrated idle tube, ai r
bleeds, idle channel restriction, idle mixture discharg e
hole, and idle mixture screws or needles (one for eac h
bore) .
\HROTTLE
VALV E
IDL EAIR/FUL
DISCHARGE HOLE
E MIXTURE
NEEDLE
OFF-IDL E
OPERATION
HOT IDLE
COMPENSATOR
VALVE
IDLE SYSTE M
Figure 11 Idle System - Typica l
The idle system operates as follows :
During curb idle (warm engine), the primary throttl e
valve is held slightly open by the idle speed screw o r
solenoid plunger . The small amount of air passing between the throttle valve and bore is regulated by adjusting the position of the speed screw or solenoid plunger to obtain the desired idle speed . Since the engine
requires very little air for idle and low speed, fuel i s
added to the air to produce a combustible mixture b y
the direct application of vacuum (low pressure) fro m
the intake manifold to the idle discharge hole below th e
throttle valve . The idle discharge hole is in a very lo w
pressure area and the fuel in the fuel chambe r
is vented to atmosphere (high pressure through the ai r
cleaner) . This causes fuel to flow from the fuel chamber
down through the main metering jet into the main fue l
well . It is picked up in the main well by the idle tube s
(one for each bore) which extend into the fuel well . The
fuel is metered at the lower tip of the submerged idl e
tube and passes up through the tube . At this point, th e
fuel is mixed with air at the top of each idle tube throug h
the top idle air bleed . The air bleed size is controlled
by either a drilled hole or a brass insert dependin g
upon carburetor application .
NOTICE: No attempt should be made t o
install a brass insert in those application s
that use a drilled hole for the top idle ai r
bleed.
Then the fuel mixture crosses over to the idle dow n
channel where it is mixed with air at the side idle bleed
located just above the idle channel restriction . The mixture continues down through the calibrated idle channe l
restriction past the lower idle air bleed and off-idl e
discharge port where it is further mixed with air . Th e
air/fuel mixture moves down to the adjustable mixture
screw discharge hole where it enters the carburetor bor e
and blends with the air passing by the slightly ope n
throttle valve . The combustible air/fuel mixture the n
passes through the intake manifold to the engine
cylinders .
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The idle mixture screws are adjustable to blend the
correct amount of air/fuel mixture from the idle syste m
to the engine at idle . Turning the mixture screws inward
(clockwise) decreases idle mixture discharge (gives a
leaner mixture) and turning the mixture screws outward
(counter-clockwise) increases idle mixture discharge
(gives a richer mixture) .
OFF-IDLE OPERATION
As the primary throttle valve is opened from cur b
idle to increase engine speed, additional fuel is needed
to combine with the extra air entering the engine . Thi s
is accomplished by the slotted off-idle discharge port .
As the primary throttle valve opens, it passes by th e
slotted off-idle discharge port, gradually exposing it to
high manifold vacuum . The mixture added from the offidle port mixes with the increasing air flow past th e
opening throttle valve to maintain the required air/fue l
mixture of the engine .
Further opening of the throttle valve increases the ai r
velocity through the carburetor venturi sufficiently t o
cause low pressure at the lower idle air bleed. As a
result, fuel begins to discharge from the lower idle ai r
bleed hole and continues throughout operation of th e
part throttle to wide-open ranges, thereby supplementin g
main discharge nozzle delivery .
The idle mixture screw discharge hole and off idl e
discharge port continue to supply sufficient fuel fo r
engine requirements until air velocity is high enough
in the venturi area to obtain efficient fuel flow from the
main metering system .
The idle system functions in a similar manner in each
carburetor bore.
The secondary throttle valves remain closed during
idle conditions and on some Quadrajet applications the y
are coated with a special graphite material which is
applied at the factory to effectively seal the secondar y
throttle valves in the bores for minimum air flow a t
idle to prevent possible rough idle.
On many exhaust emission control carburetor applications, the idle mixture screw discharge holes have bee n
reduced in size . This was done to prevent a too rich
idle adjustment in the field should the idle mixture screw s
be turned out too far beyond normal idle mixture requirements . Also, starting in 1971, idle screw limite r
caps were added to emission control carburetors to discourage adjustment of the screws in the field . On later
models, the idle mixture screws are sealed to prevent
readjustment from the factory setting in the field .
ADJUSTABLE AIR BLEE D
Another feature added to some emission carburetor s
is an adjustable off-idle air bleed system (Figure 11) . A
separate air channel is added in the air horn which leads
CANISTER
PURGE TUBE
IDLE
MIXTURE
NEEDL E
THROTTLE
VALVE
OFFIDLE
PORT
E.G .R. (EXHAUST GAS
RECIRCULATION)
IDLE DISCHARG E
HOL E
CONSTANT
CANISTER PURG E
OFF-IDLE
OPERATIO N
IDLE SYSTEM
Figure 12 Idle System - Late Model s
from the top of the air horn to the idle mixture cross
channel . An adjustment screw with a tapered head i s
mounted at the top of the channel and is used to control the amount of air bleeding into the idle system .
The off-idle air bleed is adjusted at the factory to maintain very accurate off-idle air/fuel mixture ratios . It is
adjusted during carburetor flow test and no attempt
should be made to readjust in the field . A triangular
spring clamp forced over the vent tube covers the scre w
to protect the adjustment from being tampered with an d
it should not be removed . All service air horns have this
screw preset at the factory.
FIXED IDLE AIR BY-PASS
A fixed idle air by-pass system is used on some applications which consists of air channels that lea d
from the top of each carburetor bore in the air hor n
to a point below each throttle valve . At normal idle ,
extra air passes through these channels supplementin g
the air passing by the slightly open throttle valves . Th e
purpose of the idle air by-pass system is to reduce th e
amount of air going past the throttle valves so that they
are nearly closed at idle . This reduces the amount of
air flowing through the carburetor venturi to preven t
the main discharge nozzles from feeding fuel durin g
idle operation . The triple venturi system is very sensitive to air flow and where large amounts of idle air
are needed to maintain idle speed, the fixed idle ai r
by-pass system is used .
PURGE PORTIN G
To meet evaporative emission standards on late mode l
Quadrajet applications, fuel vapors from the carburetor float bowl and fuel tank are collected in a vapo r
canister and not vented to atmosphere . On many of these
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carburetor models, vacuum ports are located in the
throttle body for canister purge . The purge ports lead
through passages to a tube in the throttle body whic h
connects by a hose to the vapor canister .
The purge ports may consist of a constant (fixed )
canister purge and a separate timed canister purge, o r
a timed canister purge only (Figure 12) .
The purge system operates as follows :
CONSTANT CANISTER PURG E
The constant canister purge port operates during idl e
operation of the engine . It is located below the throttle
valves to provide a constant purge of the canister whenever the engine is running . As the throttle valves are
opened beyond the idle position, additional purge of th e
canister is provided by each of the timed purge ports .
TIMED CANISTER PURG E
The timed canister purge ports operate during off-idle ,
part throttle, and wide-open throttle operation . They are
located above the throttle valve in each bore next to th e
off-idle discharge port . The timed purge ports supplement
the constant canister purge port (where used) to provide a
larger purge capacity for the vapor canister and to pre vent over-rich mixtures from being added to the carburetor metering at any time.
On some applications (see Figure 12), the constant
purge port is used as the vacuum source to the Earl y
Fuel Evaporation (E.F.E.) Valve located in the exhaust
manifold . On these models, purging of the canister i s
accomplished through the Positive Crankcase Ventilation
(P.C.V.) system .
EXHAUST GAS RECIRCULATIO N
An Exhaust Gas Recirculation (E .G.R.) system, consisting of an E.G.R. Valve, separate back-pressure
transducer valve (where used), vacuum hoses, an d
vacuum supply ports in the Quadrajet carburetor, i s
used on many vehicle applications to meet exhaust
emission requirements . The E.G.R. valve is operate d
by a vacuum signal taken from the carburetor . The
vacuum signal, dependent upon application, is taken
from one or two punched ports located in the carburetor bore just above the throttle valves . Thus, E.G.R.
valve operation is "timed " for metering exhaust gases
to the intake manifold dependent upon location of th e
ports in the carburetor primary bore and by the degree
of throttle valve opening (See Figure 12) .
It is important that the E .G.R. vacuum signal port(s )
not be exposed to manifold vacuum during engin e
idle and deceleration to keep the E .G.R. valve closed.
This prevents rough idle which can be caused by excessive exhaust gas contamination in the air/fuel mixtures.
TRANSMISSION CONVERTER CLUTC H
Some applications have a port located above th e
throttle valve that is used to supply a timed vacuu m
source for the automatic transmission converter clutch
(see car division service manual for description of thi s
transmission feature .)
HOT IDLE COMPENSATO R
The Hot Idle Compensator, when used on 4MV-4MC M4MC Quadrajet carburetors (See Figure 11), is locate d
in a chamber at the rear of the carburetor float bow l
adjacent to the secondary bores . Its purpose is to offset
the enriching effects caused by excessive fuel vapor s
during hot engine operation.
The compensator consists of a thermostatically-controlled valve, a heat sensitive bi-metal strip, and a valv e
holder and bracket . The compensator valve assembly is
held in place by a dust cover over the valve chamber .
A seal is used between the compensator valve and th e
float bowl casting . The valve closes off an air channel
leading from a hole in the top of the air horn, jus t
beneath the air cleaner, to a point below the secondar y
throttle valves.
Normally, the compensator valve is held closed by
tension of the bi-metal strip. During extreme hot engine
operation, excessive fuel vapors entering the engine
manifold cause richer than normally required mixtures ,
resulting in rough engine idle and stalling. At a predetermined temperature, when extra air is needed to
offset the enriching effects of these fuel vapors, th e
bi-metal strip bends and unseats the compensator valve .
This uncovers the air channel leading from the valve
chamber to the point below the throttle valves . This
allows enough air to be drawn into the engine manifol d
to offset the richer mixtures and maintain a smoot h
engine idle . When the engine cools and the extra air i s
not needed, the bi-metal strip relaxes, closes the valve ,
and operation returns to normal mixtures .
For proper idle adjustment when the engine is hot ,
the compensator valve must be closed . To check this, a
finger may be held over the compensator air inlet
channel located on top of the air horn . If no drop in
engine RPM is noted on a tachometer, the valve is
closed. If the valve is open, plug the hole or cool engine
down to a point where the valve automatically closes fo r
proper idle adjustment .
NOTICE : Plug the compensator hole with a
pencil or something that will be seen, as
the plug must be removed before the air
cleaner is installed . Otherwise the compensator will not function if the plug is left i n
the hole .
On some applications, the air inlet to the hot
idle compensator is located beneath the air
valve in the secondary bores . The air inlet i n
this location improves idle quality when the
I
9D-5
March 198 1
Page 1 2
feeds additional fuel at closed choke for good cold engine
starting . Calibrated air bleeds, located in the air horn ,
are used with this system .
The air-velocity sensitive pull-over enrichment system
allows the use of slightly leaner mixtures during par t
throttle operation and still provides enough fuel durin g
high speed operation . This feature gives added refinement to the fuel mixtures for exhaust emission control .
FIXED JET
MAIN METERIN G
RODS (2)
MAIN METERING
JETS (2 )
FIXED JE T
MAIN WELL AIR BLEED TUBE S
Some 4MV Quadrajet applications use Main Wel l
Air Bleed Tubes in place of the main well air blee d
holes (Figure 16) . The tubes, extending further into eac h
primary bore, help main discharge nozzle response a s
the main metering system starts to feed fuel .
MAIN METERING SYSTEM M4MC-M4M E
MODELS
Starting in the 1975 model year, major casting change s
were made to the air horn, float bowl, and throttl e
body of the Quadrajet carburetor to incorporate a ne w
Adjustable Part Throttle (A .P .T .) feature and, on som e
applications, the addition of an auxiliary power piston
and metering rod assembly. These new models were
termed " modified" and designated by the prefix "M"
to the model listing (e .g ., M4MC) .
A .P .T . METERING ROD ASSEMBLIES [Modified Design )
Figure 17 Adjustable Part Throttle - Modifie d
Model s
MAIN WELL AI R
BLEEDS
FACTORY-METERING
ADJUSTMENT SCREW
MAIN POWER PISTON
(DOWN)
POWER PISTON
SPRING
f
r' THROTTLE VALVES
I
VACUUM MAIN
METERING
PASSAGE JET
S
MAI N
METERING
ROD S
MAIN METERING SYSTE M
ADJUSTABLE PART THROTTLE
The A .P.T . feature on these " modified " models consists of an adjustable metering rod assembly with fille r
spool (Figure 17-A) or combination aneroid - meterin g
rod assembly (for an explanation of aneroid, see Altitud e
Compensation, below) . The adjustable metering rod ,
with or without aneroid, provides close tolerance contro l
of fuel flow to the main metering system during th e
part throttle range .
The A .P .T . adjustment is performed at the factor y
during flow test by turning the threaded metering rod ,
or aneroid-metering rod assembly, up or down to position
the metering rod in a fixed metering jet located at th e
bottom of the fuel reservoir in the float bowl . This set s
the part throttle air/fuel mixture to the desired flow band .
ALTITUDE COMPENSATIO N
On M4MCA-M4MEA models, a barometric pressure sensitive aneroid, sometimes called a "bellows", is included as an integral part of the threaded A .P .T .
metering rod assembly (Figure 17-B) . The aneroid, being
sensitive to air pressure change, automatically eithe r
expands or contracts with changes of altitude to lowe r
or raise the metering rod in the fixed metering jet to
maintain control of part throttle air/fuel ratios .
Figure 18 Separated Main Well s
NOTICE : The position of the A .P.T . metering rod in the fixed jet is extremely critical .
Adjustment should NEVER be attempted
unless a replacement is required . The threaded
A .P .T . metering rod should be adjuste d
carefully following adjustment procedures (Se e
step 7a, page 38) .
As a result of these changes, a new float assembly ,
plastic filler block (located in the top of the float chamber over the float valve), and new air horn gasket ar e
used with the "modified" carburetor models .
SEPARATED MAIN WELLS
The main metering system of most later "modified "
Quadrajet models (Figure 18) operates similarly to tha t
described for 4MV-4MC models, above, except the float
bowl casting is revised to provide for separated main
wells . The separated main well feature is used to feed
each main nozzle for improved fuel flow through the
carburetor venturi . On these models, a special aneroi d
cavity insert is used in the fuel chamber to replace the
adjustable metering rod assembly with filler spool, or
aneroid-metering rod assembly, formerly used .
9D. 5
March 198 1
Page 1 3
ADJUSTABLE PART THROTTLE FEATUR E
On "modified" Quadrajet carburetors that use separated main wells, the A .P .T . adjustment consists of a
pin pressed in the side of the power piston which ex tends through a slot in the side of the piston well . When
the power piston is down (economy position), the pi n
stops on top of a flat surface of the adjustment scre w
located in a cavity next to the power piston (See Figur e
18) . The adjustment screw is held from turning by a
tension spring beneath the head of the screw .
During production flow test, the adjustment screw i s
turned up or down which, in turn, places the tapere d
metering rod at the exact point in the metering jet orifice
to obtain the desired air/fuel mixture ratio to meet
exhaust emission requirements .
NOTICE : The A .P .T . screw is preset at the
factory and no attempt should be made t o
change this adjustment in the field . If a float
bowl replacement is required during carburetor service, the new service float bowl assembly will be supplied with the adjustment
screw preset as required .
POWER SYSTE M
The power system in the Quadrajet carburetor provides extra mixture enrichment to meet power requirements under heavy engine loads and high-speed operation . The richer mixtures are supplied through th e
main metering system in the primary and secondar y
sides of the carburetor (Figure 19) .
The fuel mixture is enriched in the two primary bores
through the power system . This consists of a vacuu m
operated power piston and a spring(s) located in a cylinder connected by a passage to intake manifold vacuum .
The spring(s) under the power piston apply an upwar d
force against manifold vacuum force tending to pull th e
piston downward .
During part throttle and cruising ranges, manifol d
vacuum is sufficient to hold the power piston dow n
against spring force so that the larger diameter of th e
primary metering rod tip is held in the main meterin g
jet orifice to provide leaner mixtures during these period s
of engine operation . However, as the engine load i s
increased to a point where extra mixture enrichment i s
required, the power piston spring force overcomes the
vacuum pull on the power piston and the tapered ti p
of the primary metering rod moves upward in the mai n
metering jet orifice . The smaller diameter of the metering
rod tip allows more fuel to pass through the main metering jet and enrich the fuel mixture to meet the adde d
power requirements . As engine load decreases, the manifold vacuum rises and extra mixture enrichment is n o
longer needed . The higher vacuum pulls downward o n
the power piston against spring force which moves th e
larger diameter of the metering rod into the metering
AIR VALVE S
(OPE N I
POWER PISTON
MAI N
SPRING
METERIN G
VACUUM JET S
PASSAGE
METERING MAIN
-SECONDARY
DISCS DISCHARGE THROTTLE VALVE S
MAIN
NOZZLES
METERING
RODS
POWER SYSTEM
Figure 19 Power Syste m
jet orifice returning the fuel mixture to normal econom y
ranges .
Dual power piston springs are used beneath the powe r
piston in the piston bore of some 4MV-4MC Quadrajet
models (Figure 19) . A smaller diameter power pisto n
spring seats in the center of the piston and bottom s
on the float bowl casting . The spring is used to control
power enrichment during light engine loads . A larger
diameter spring surrounds the smaller inner spring an d
exerts additional pressure on the bottom of the powe r
piston to provide efficient mixture ratios at heavier engin e
load conditions . The dual power piston spring feature ,
on models so equipped, assists in providing improve d
fuel control of air/fuel mixture ratios to meet emissio n
and power requirements of the engine .
POWER SYSTEM - MECHANICA L
OPERATIO N
Some Quadrajets have a mechanical power enrichmen t
system in addition to the vacuum enrichment feature .
This provides accurate control of fuel mixtures at hig h
engine speeds and load and yet allows the use of vacuu m
enrichment for improved fuel control during mediu m
engine loads .
The mechanical enrichment is controlled by a stem
pressed into the base of the power piston which extend s
into the throttle body . The stem is operated by a leve r
which is hinged to the throttle body casting and a ca m
on the center of the throttle shaft . When the throttle
valves are opened to a pre-determined point, the ca m
on the throttle shaft forces the lever upward until i t
contacts the stem on the power piston and pushes th e
complete piston assembly upward against engine vacuu m
(Figure 20) . This, in turn, lifts the metering rods ,
placing the smaller diameter of the metering rods in
the main metering jets for positive mixture enrichmen t
at greater throttle valve openings .
The power piston has a "trapped" spring which limit s
the travel of the piston during vacuum operation . The
spring is retained between the piston and a flute d
9D-5
March 198 1
Page 14
POWER
PISTON (UP )
SECONDARY METERING ROOS (2)
AUXILIARY
METERING ROD (I)
MAI N
MAIN
POWE R
METERING PISTON (UP)
ROOS 121
ACCELERATOR
WELL & TUB E
ACCELERATING WELL POR T
METERIN G
ROD LEVER
POWER SYSTE M
MECHANICAL POWER SYSTEM
Figure 20 Mechanical Power Enrichmen t
washer on the power piston stem . The washer is retained with a "C" clip located in a groove on the powe r
piston stem .
During high engine vacuum, the power piston sprin g
is compressed and the fluted washer and piston are
seated at the bottom of the power piston cavity . A s
engine load increases, vacuum drops and the powe r
piston moves upward against spring tension until th e
" C" clip seats against the fluted washer . No more enrichment will take place until the pin in the power pisto n
is contacted by the mechanical enrichment lever . As
the throttle valves are opened further, the complet e
power piston assembly is forced upward placing th e
smaller diameter of the metering rods in the jets fo r
maximum enrichment at higher engine speeds and loads.
When engine load and speed is decreased, the power
piston will return to the down position, seating th e
fluted washer and piston in the bottom of the power
piston cavity as high engine vacuum compresses th e
power piston spring . This returns the metering syste m
to leaner fuel mixtures for light engine loads .
MULTIPLE STAGE POWER ENRICHMEN T
In some "modified" Quadrajet carburetors, a multipl e
stage power enrichment system, consisting of two powe r
pistons (Figure 21), is used for more sensitive control of
air/fuel ratios during light duty engine power requirements while providing for richer mixtures durin g
moderate to heavy engine loads .
Figure 21 Multiple Stage Power Syste m
which lifts the single metering rod out of a fixed meterin g
jet . This provides partial fuel enrichment for light dut y
engine loads .
MAIN (PRIMARY) POWER PISTO N
During moderate to heavy engine loads when a furthe r
drop in manifold vacuum occurs with increased throttl e
opening, the main (rear) piston spring force overcome s
the vacuum pull and raises the piston which lifts th e
two metering rods out of the metering jets for additional
fuel enrichment for heavy duty power requirements .
The multiple stage (two piston) power enrichmen t
system is specifically calibrated for the power requirements of each engine by controlling spring rates of each
piston . The system requires no adjustment in the field ;
however, the main (rear) power piston and metering
rod assemblies and the auxiliary (front) power pisto n
and metering rod assembly are removable for norma l
cleaning and service replacement as needed .
NOTICE : The main (rear) and auxiliary
(front) power piston springs must NOT b e
interchanged . To prevent mixing of powe r
piston springs at time of carburetor disassembly, lightly wrap a piece of masking tap e
around the auxiliary power piston spring fo r
identification . Then, on reassembly, remov e
the tape and install the spring in the fron t
location beneath the auxiliary power pisto n
with single metering rod .
AUXILIARY POWER PISTO N
POWER SYSTEM TURBOCHARGER APPLICATION S
An auxiliary power piston and single metering rod
assembly, located in front of the main (primary) powe r
piston, is used for light duty power requirements . O n
light throttle opening when manifold vacuum drops t o
a predetermined point, the spring force under the auxiliar y
piston overcomes the vacuum pull and raises the piston
Some modified Quadrajet models are designed for
Turbocharger applications . The power system in thes e
models operates in the same manner as previousl y
described except for one important difference . Th e
vacuum supply, directed to the underside of the powe r
piston, is controlled externally by a Turbocharger Vacu-
9D- 5
March 198 1
Page 1 5
SECONDAR Y
ACCELERATO R
WELLS & TUBE S
to meet engine demands . The secondary stage of the
carburetor provides the additional air and fuel throug h
the secondary throttle bores for power and performanc e
requirements .
The secondary stage has a separate and independent metering system (Figure 22) . It consists of two
large throttle valves connected by a shaft and linkage
to the primary throttle shaft . Fuel metering is controlle d
by a spring-loaded air valve, secondary metering orific e
plates, secondary metering rods, fuel wells with blee d
tubes, fuel discharge nozzles, accelerating wells an d
tubes . These are used to modify fuel flow characteristics
for exact air/fuel calibration .
SECONDARY METERIN G
ORIFICE PLATES SECONDAR Y
DISCHARG E
NOZZLE S
SECONDARY SYSTEM (Typical)
Figure 22 Secondary System - Typica l
urn Bleed Valve . The vacuum signal is routed to th e
carburetor through a hose from the bleed valve to a n
external tube located on the side of the carburetor .
The power system operates as follows :
During part throttle and cruising ranges, engine loa d
is light and vacuum, from the Turbocharger Vacuu m
Bleed Valve, is sufficient to hold the power piston dow n
against spring force and the larger diameter of th e
metering rod tip is held in the metering jet for leane r
mixtures .
As engine load is increased to a point where extra
fuel enrichment is required and the intake manifold i s
pressurized by the exhaust gas driven Turbocharger ,
the vacuum bleed valve " switches " and reduces vacuu m
to the power piston to zero . At this point, spring forc e
operating on the power piston lifts the main meterin g
rods for increased fuel delivery .
The remote power enrichment feature, through the
vacuum bleed valve, provides richer mixtures during
heavy engine loads and wide-open throttle power requirements when the intake manifold is pressurized b y
the Turbocharger at a time when manifold vacuum i s
high enough tending to operate the power piston in th e
normally " lean " position . In this way, the power syste m
controls fuel metering during light and heavy powe r
requirements .
The secondary metering system supplements fue l
flow from the primary stage and operates as follows :
When the engine reaches a point where the primary
bores cannot meet engine air and fuel demands, a leve r
on the primary throttle shaft, through a connecting
link to the pick-up lever on the secondary throttle shaft ,
begins to open the secondary throttle valves . This occurs
only if the choke has warmed the thermostatic coi l
sufficiently to release the secondary throttle valve lock out lever (if used) .
As the secondary throttle valves open, engine manifold vacuum (low pressure) is applied directly beneath
the air valves . Atmospheric pressure on the top of th e
air valves forces the air valves open against spring an d
air valve dashpot forces, provided the choke coil has
warmed sufficiently to release the air valve lockout lever,
if used . This allows air to pass through the secondar y
bores of the carburetor .
SECONDARY SYSTE M
On most models, accelerating wells are used to supply
fuel immediately to the secondary bores . This prevent s
a momentary leanness until fuel begins to feed from th e
secondary discharge nozzles. When the air valves begi n
to open, the upper edge of each valve passes the accelerating well ports (one for each bore) . As the edge s
of the air valves pass the ports, they are exposed to
manifold vacuum and immediately feed fuel from th e
accelerating wells located on each side of the fuel chamber . Each accelerating well has a calibrated orific e
which meters the fuel supplied to the well from th e
fuel chamber . Some models have the accelerating wel l
ports located beneath the front edge of the air valve
instead of above . These begin to feed fuel to the secondary bores almost instantly after the secondary throttl e
valves open and before the air valves begin to open .
This type of porting is used on some models wher e
added enrichment is needed during cold operation
when the air valve is locked closed, and also provide s
an earlier cut-in of fuel from the ports than the model s
which have the port located above the valves . The use
of either type of porting is dependent upon engine fuel
demands .
The primary stage of the Quadrajet carburetor provides adequate air and fuel for low speed operation .
However, at higher speed, more air and fuel are needed
The secondary main discharge nozzles (one for each
bore) are located just below the center of the air valve s
9D-5
March 198 1
Page 1 6
and above the secondary throttle valves . The nozzles ,
being located in a low pressure area, feed fuel as follows :
As the secondary throttle valves are opened, atmospheric pressure opens the air valves . This rotates a
plastic eccentric cam attached to the center of the air
valve shaft . As the cam rotates, it lifts the secondary
metering rods out of the secondary orifice plates throug h
the metering rod hanger which follows rotation of th e
eccentric cam .
Fuel flows from the fuel chamber through the secondary metering orifice plates into the secondary main
wells where it is mixed with air from the secondar y
main well air bleed tubes . The air emulsified fuel
mixture travels from the main wells through the secondary discharge nozzles where it sprays into the secondar y
bores . Here the fuel is mixed with air traveling throug h
the secondary bores to supplement the air/fuel mixture
delivered from the primary bores and goes on into th e
engine as a combustible mixture .
As the secondary throttle valves are opened furthe r
and engine speeds increase, air flow through the secondary side increases and opens the air valves to a greate r
degree which, in turn, lifts the secondary meterin g
rods further out of the orifice plates . The metering rod s
are tapered so that the fuel flow through the secondar y
metering orifice plates is directly proportional to ai r
flow through the secondary carburetor bores . In thi s
manner, correct air/fuel mixtures through the secondar y
bores are controlled by the depth of the metering rod s
in the orifice plates .
The depth of the metering rods in the orifice plate s
in relation to the air valve position are factory adjuste d
to meet air/fuel requirements for each specific engin e
model — no change in this adjustment should be mad e
in the field . Also, many models include a tang on th e
air valve lever which contacts a stop on the air hor n
casting to control carburetor air flow capacity.
METERING RODS - PRIMAR Y
There are two types of primary main metering rods
used in the Quadrajet carburetors . 1968 and late r
models use a rod which has a double or multiple tape r
at the metering tip . The 1967 and earlier models have a
single taper at the metering tip .
Both rod types use a similar two-digit numbering
system . The number indicates the diameter of th e
metering rod and is the last two digits of the part number. The 1968 and later models will have a letter stampe d
on the rod after the two-digit number.
METERING RODS - SECONDAR Y
The secondary rods are coded with a two-letter system which corresponds directly to the part number .
(See Delco Bulletin 9A-100 for a complete description and listing of metering rods) .
There are other features incorporated in the secondary
metering system as follows :
1. The secondary main well air bleed tubes exten d
downward into the main fuel well below normal fue l
level . These bleed air into the fuel in the secondar y
wells to quickly emulsify the fuel with air for good
atomization and improved fuel flow from the secondar y
nozzles .
2. The secondary metering rods may have a milled
slot at the larger diameter of the metering tip . Th e
purpose of the slots is to ensure an adequate supply o f
fuel in the secondary main wells when the air valves ar e
in the closed position . At this point, the metering rod s
are nearly seated against the metering orifice plates .
The slot in the rod is adjacent to the orifice plate an d
allows a small amount of fuel to pass between the meter ing rod and metering disc . During extreme hot engine
idle or hot soak, the fuel could boil out of the secondar y
fuel wells . The milled slot allows enough fuel to bypass the orifice plate and keep the main fuel wells ful l
of fuel . This ensures adequate fuel supply in the mai n
wells at all times to give immediate fuel delivery fro m
the secondary discharge nozzles .
3. Some applications use secondary discharge nozzle s
that incorporate a vertically drilled cross hole located
about half way down the length of the nozzle . The
hole serves as an additional air bleed to assist air/fue l
mixture distribution passing through the secondary
discharge nozzle .
4. A baffle plate, extending into each secondary bore ,
is located just below the air valves on all models . The
baffle extends up and around the secondary discharg e
nozzles to provide equal fuel distribution, as near a s
possible, to all engine cylinders at lower air flows .
5. On some models, an integral baffle is added t o
the bottom side of the secondary air valve . The baffle
improves mixture distribution from the secondary side
at higher air flows .
6. An air horn baffle is used on some models to
prevent incoming air from the air cleaner reacting o n
the secondary main well bleed tubes . The baffle is located adjacent to the secondary well bleed tubes an d
extends above the air horn between the primary an d
secondary bores . This prevents incoming air from forcin g
the fuel level down in the secondary wells through th e
bleed tubes and prevents secondary nozzle lag on heav y
acceleration .
7. Some models use notched secondary air valves t o
reduce the vacuum signal at the nozzles for leaner air/
fuel mixture ratios during initial air valve opening . Th e
leaner mixtures assist in meeting emission requirement s
and also improve throttle response when operating at
high altitudes .
AIR VALVE DASHPO T
The secondary air valves use an air valve dashpot
9D.5
March 1981
Page 1 7
Delco
AIR VALVE CLOSING SPRIN G
LEVE R
PUM P
LEVER
n
r
/
LIN K
PISTON ~~.
STEM
rlu
~~.
'HINGE
PIN
DISCHARG E
yy PASSAG E
DISCHARG E
BALL RETAINER
AIR VALVE DASH POT OPERATION (EARLY )
AIR VALVE SHAFT LEVE R
CLOSE D
OPEN ±'
ACTUATING RO D
VACUUM BREAK
DIAPHRAGM ASSEMBLY
AIR VALVE DASHPO OPERATION (LATE )
Figure 23 Air Valve Dashpot Design s
feature to control opening rate of the air valve . This
prevents an uncontrolled air valve opening rate whic h
results in an instantaneous air rate change and a " lagging" fuel rate change as the secondary throttle
valves are opened . The dashpot, through linkage, controls opening of the air valves to provide a smoot h
transition to secondary system operation .
There are two different types of air valve dashpot s
used in the Quadrajet carburetor :
The early type dashpot (Top of picture, Figure 23 )
consists of a piston which operates in a fuel well adjacen t
to the float bowl . The piston stem is connected to th e
air valve through a link and lever assembly . As the air
valves open, the dashpot piston is pulled upward forcin g
fuel to flow between the side of the piston and fue l
well which retards the air valve opening . A rubbe r
washer attached to the piston stem acts as a check valve .
During upward movement of the piston, the rubbe r
washer seats and forces all fuel to flow around the piston .
When the air valve closes, the check valve unseats an d
allows fuel to also pass through the center of the pis ton allowing the air valves to return closed rapidly .
The late type air valve dashpot (Lower picture, Figur e
23) operates off of the front choke vacuum break diaphragm unit . The secondary air valve is connected t o
the choke vacuum break unit by a rod, to control the
opening rate of the air valve. Whenever manifold vacuu m
is sufficiently high, the vacuum diaphragm is seated ,
plunger retracted, against spring load . At this point ,
the vacuum diaphragm link is in the forward end of th e
slot in the air valve lever, or in the rear of the slot i n
the vacuum diaphragm plunger, and the air valves ar e
closed .
PUMP
PLUNGER
PUMP DISCHARGE
RETURN CHECK BALL
SPRIN G
EXPANDE R
SPRIN G
PUMP SYSTEM
Figure 24 Pump Syste m
During acceleration or heavy engine loads when th e
secondary throttle valves are opened, the manifol d
vacuum drops . The spring located in the vacuum diaphragm unit overcomes the vacuum force and move s
the plunger stem outward . This action allows the air
valves to open . The opening rate of the air valves i s
controlled by the calibrated restriction in the vacuum
inlet of the diaphragm cover and the valve closing spring .
The dashpot action, due to this restricted vacuum flow
and spring force, provides the required delay in ai r
valve opening needed until sufficient fuel flows from
the secondary discharge nozzles .
ACCELERATING PUMP SYSTEM
During quick accelerations when the throttle i s
opened rapidly, air flow through the carburetor bore s
and intake manifold vacuum change almost instantaneously . However, the fuel which is heavier, tends to
lag behind causing a momentary leanness . To preven t
this, the accelerator pump system is used to provid e
the extra fuel necessary for a smooth transition in engine
operation during this period .
The accelerating pump system is located in the primar y
stage of the carburetor . It consists of a spring-loade d
pump plunger and pump return spring (operating in a
fuel well), fuel passage, discharge check ball, retainer ,
and pump jets, one in each bore (Figure 24) .
On most late Quadrajet models, an expander (garter)
spring is used in the pump cup for constant pump cu p
to pump wall contact . The pump cup is of the floating
design ; i .e ., the up and down movement of the cup o n
the plunger head either " seats " to provide a solid charge
of fuel on the down-stroke, or " unseats " on the filling
of the pump well (up-stroke) . The cup remains unseate d
when there is no pump plunger movement which allows
vapor to vent from the pump well .
9D•5
March 198 1
Page 18
Delco
CHOKE ENRICHMENT
FUEL CHANNE L
CHOKE VALVE
_ CHOKE ROD
/-`
I r-)
FAST IDLE CA M
VACUUM BREA K
LEVER AND TANG
VACUUM BREAK
ASSEMBL Y
P
'-~--UNIOADER TANGS
FAST IDLE SCREW
4M-2 5
Figure 25 Pump Stem Seal & Retaine r
The pump plunger is operated by a pump lever on
the air horn which is connected directly to the throttl e
lever by a rod .
When the pump plunger moves upward in the pump
well as happens during throttle closing, fuel from th e
fuel chamber enters the pump well through a vertical
slot located near the top of the pump well . It flow s
past the " unseated " pump cup to fill the bottom of
the pump well and pump discharge passage .
When the primary throttle valves are opened, th e
pump rod and lever forces the pump plunger downward .
The pump cup seats instantly and fuel is forced throug h
the pump discharge passage where it unseats the pump
discharge check ball and passes on through the passag e
to the pump jets where it sprays into the venturi are a
of each primary bore .
It should be noted the pump plunger is spring loaded .
The upper duration spring is balanced with the bottom
pump return spring so that a smooth, sustained charge
of fuel is delivered during acceleration . Selection of the
duration spring by the factory is used to control th e
differences in rate of movement between the pump
linkage and the plunger head for correct pump fue l
delivery .
The pump discharge check ball seats in the pump
discharge passage during upward motion of the pump
plunger so that air will not be drawn into the passag e
and prevent proper pump fill .
During higher air flows through the primary bores ,
a vacuum exists at the pump jets . A passage, locate d
just behind the pump jets, leads to the top of the ai r
horn to vent the pump fuel circuit outside the carburetor
bores . This acts as a suction breaker so that when th e
pump is not in operation, fuel will not be pulled out o f
the pump jets into the venturi area . This insures a full
pump stream when needed and prevents any fuel " pull over" from the pump discharge passage .
Figure 26 Choke System-4M V
In order to keep evaporative emission levels to a
minimum, later model M4ME-M4MC models have a
pump plunger stem seal and retainer located in the ai r
horn . In the event of service repair or cleaning of th e
carburetor, a new seal and retainer should be installe d
(See Figure 25) .
CHOKE SYSTE M
The Quadrajet choke valve is mounted in the air
horn located above the carburetor primary venturi . A
closed choke valve provides the correct air/fuel mixtur e
enrichment to the engine for good cold engine startin g
and when partially open smooth running during th e
warm-up period . The secondary throttle valves, or air
valve on some models, are locked closed until the engine
is thoroughly warm and the choke valve is wide open .
The Model 4MV choke system (Figure 26) consists of
a choke valve, vacuum break diaphragm assembly ,
thermostatic coil-mounted on the intake or exhaust
manifold, fast idle cam, and connecting linkage .
Heat from exhaust gases is used for control of thermostatic coil temperature . Choke operation is controlle d
by a combination of intake manifold vacuum, the off set choke valve, temperature, and throttle position .
The thermostatic coil is calibrated to hold the choke
valve closed when the engine is cold .
The choke system operates as follows :
When the engine is cold, prior to starting, depressin g
the accelerator pedal to the floor opens the carburetor
throttle valves . This allows the fast idle cam followe r
lever to clear the steps on the fast idle cam . At this
point, torque from the thermostatic coil closes the choke
valve and rotates the fast idle cam so that the cam follower lever comes to rest on the highest step of th e
fast idle cam . (This opening of the throttle valves also
9D . 5
March 198 1
Page 1 9
Delco
pumps a priming mist of fuel through the pump jets
into the primary throttle bores to aid starting) . During
cranking, engine vacuum below the choke valve pull s
fuel from the idle system and main discharge nozzles .
This provides adequate enrichment for good cold starts .
Some Quadrajet models use a choke enrichment fue l
system to supplement fuel feed from the primary mai n
discharge nozzles for good cold engine starting .
Two calibrated holes, one in each primary bore, ar e
located in the air horn just BELOW the choke valv e
to supply added fuel for cold enrichment during th e
cranking period . The extra fuel is supplied throug h
channels which lead to the secondary accelerating wel l
pickup tubes to allow fuel at closed choke to be draw n
from the secondary accelerating wells located in the float
bowl chamber, (As shown in Figure 26) . Also, during
warm engine operation, the two calibrated holes in th e
air horn feed a small metered amount of fuel at higher
air flows to supplement fuel flow in the primary bore s
to provide the extra fuel needed at higher engine speeds .
As mentioned earlier (See Main Metering System) ,
other Quadrajet models use the fuel pull-over enrichment system . This system is similar to the choke
enrichment fuel system except that two calibrated holes ,
one in each primary bore, are located in the air hor n
just ABOVE the choke valve to supply added fuel durin g
higher carburetor air flows . The calibrated holes, locate d
above the choke valve, do not feed fuel at closed chok e
during the engine cranking period .
When the engine starts and is running, manifol d
vacuum is applied to the vacuum break diaphragm
unit mounted on the side of the float bowl . This move s
the diaphragm plunger in until it strikes the rear cover ,
thereby opening the choke valve to a point where the
engine will run without loading or stalling . (This is called
the " vacuum break " position) . At the same time, the
fast idle cam follower lever on the end of the primary
throttle shaft will drop from the highest step on th e
fast idle cam to a lower step when the throttle is opened .
This gives the engine sufficient fast idle and correc t
fuel mixture for running until the engine begins t o
warm up and heat the thermostatic coil .
As the engine continues to warm up, heat gradually
relaxes tension of the thermostatic coil to allow th e
choke valve to continue opening through air pressur e
pushing on the offset choke valve and the weight of th e
linkage pulling the choke valve fully open at which poin t
the engine can run at normal air/fuel mixtures .
The fast idle cam has graduated steps so that the fas t
idle speed is lowered gradually during the engine warmup period . The fast idle cam movement (and ste p
position) is a function of choke valve position . Whe n
the engine is warm and the choke valve is completel y
open, the fast idle cam follower will be off the step s
of the fast idle cam . At this point, the idle speed scre w
or solenoid controls normal (warm) engine idle speeds .
SECONDAR Y
LOCKOUT LEVER
FAST IDLE CAM
FOLLOWER
CHOKE SYSTEM (WITH SECONDAR Y
LOCKOUT FEATURE)
4M-2 6
Figure 27 Secondary Throttle Valve Lockou t
SECONDARY THROTTL E
VALVE LOCKOUT
A secondary throttle valve lockout feature is used o n
many Quadrajet models to prevent opening of the secondary throttle valves during cold operation when wide open accelerations could cause possible engine damag e
or excessive wear (Figure 27) . On these applications ,
a lockout lever, located on the float bowl, is weighte d
so that a tang on the lower end of the lever catches a
lock pin on the secondary throttle shaft and keeps th e
secondary throttle valves closed . As the engine warms
up, the choke valve opens and the fast idle cam drops .
When the engine is thoroughly warm, the choke valv e
is wide open and the choke coil pulls the intermediat e
choke lever completely down and the fast idle ca m
drops down so that the cam follower is completely of f
the steps of the cam . As the cam drops the last fe w
degrees, it strikes the secondary lockout lever and pushe s
it away from the secondary valve lockout pin . This
allows the secondary throttle valves to open and operat e
as described under the Power System .
AIR VALVE LOCKOU T
Some Quadrajet carburetors incorporate an air valv e
lockout feature (Figure 28), instead of the secondar y
throttle valve lockout, whereby the air valves are locke d
closed until the engine is thoroughly warm and the
choke valve is wide open . An air valve lockout lever ,
mounted on the air horn, is so weighted that a tang o n
the lever catches the upper edge of the air valve an d
keeps the air valves closed when the choke valve is closed.
When the thermostatic coil warms up it moves the chok e
valve toward the open position, the end of the choke
rod moves upward and strikes a tang on the air valv e
lockout lever . As the choke rod moves up to the end o f
its travel, it pushes the lockout tang upward and unlocks the air valve .
9D• 5
March 198 1
Page 20
Delc o
AIR VALVE
SHAFT LEVER
VACUUM BREAK
7ADJUSTMENT TANG
VACUUM BREA K
ASSEMBL Y
% ~ VACU U
+^~ BREAK
ASSEM Y
/ /
THERMOSTATIC
COIL AND ROD
!j-w`~
11 UNLOADER
TANGS
FAST IDLE SCREW
CHOKE SYSTEM
4M-27
Figure 28 Air Valve Lockou t
Also, some early model 4MV carburetors use a vacuu m
break modulating spring and split choke spring (Figur e
28) . The vacuum break modulating spring allows th e
vacuum break (choke valve position) to vary accordin g
to ambient temperature . The vacuum break modulating
spring, connected to the vacuum break link, allow s
varying choke openings depending on the closing force
of the thermostatic coil . As the closing force of the coil
increases (cool weather), the link is allowed to move i n
the slotted lever until the modulating spring overcomes
the coil force, or the link is in the end of the slot . This
results in less vacuum break during cooler weathe r
and more vacuum break during warmer weather .
The split choke feature operates during the last few
degrees of choke thermostat rotation . The purpose is to
maintain the fast idle speed long enough to keep th e
engine from stalling, but allow the use of a choke coi l
which lets the choke valve open quickly . The operatio n
of the split choke feature is controlled by a torsion spring
on the intermediate choke lever shaft . As explaine d
earlier, air pressure action on the offset choke valv e
tends to force the choke valve open against tension o f
the choke thermostatic coil . In the last few degree s
of thermostatic coil opening motion, a tang on the inter mediate choke lever contacts the end of the torsio n
spring . This keeps the fast idle cam follower lever o n
the last step of the fast idle cam longer to maintain
fast idle until the engine is thoroughly warm . The spring
works against the thermostatic coil until the coil is hot
enough to pull on the intermediate choke lever and over come the torsion spring tension . The torsion sprin g
must be placed in the specified notch in the vacuum
break mounting bracket for application used .
On all 4MV models, the choke system is equippe d
with an unloader mechanism which is designed to partially open the choke valve, should the engine becom e
loaded or flooded . To unload the engine, the accelerator
pedal must be depressed so that the throttle valves ar e
held wide open . A tang on a lever on the choke side of
SECONDAR Y
LOCKOUT LEVER
FAST IDLE CAM
FOIIOWER
4M-28
Figure 29 Spring Assist Choke Closing Syste m
the primary throttle shaft contacts the fast idle ca m
and through the intermediate choke shaft forces the
choke valve slightly open . This allows extra air to ente r
the carburetor bores and pass on into the engine manifold and cylinders to lean out the fuel mixture so tha t
the engine will start .
CHOKE SYSTEM WITH SPRING ASSIS T
CHOKE CLOSING SYSTE M
Some 4MV carburetors use a spring assist chok e
closing system (Figure 29) . The assist spring is of the
torsion type and is added to the intermediate choke
shaft . It exerts pressure on the vacuum break lever t o
force the choke valve toward the closed choke position .
The tension of the torsion spring is overcome by th e
choke thermostatic coil located on the engine manifol d
which, during the engine warm up period, will pull th e
choke valve open . The addition of a torsion spring
assists in closing the choke valve to ensure good engine
starting when the engine is cold .
Along with the choke closing assist spring, certai n
4MV models use the fast idle cam " pull-off" feature .
When the engine starts and is running, manifol d
vacuum is applied to the vacuum break diaphragm an d
the diaphragm plunger moves slowly inward to ope n
the choke valve . As this happens, a tang on the plunge r
contacts the end or "tail" of the fast idle cam to " pull off" the cam from the high step to the lower secon d
step setting .
A slight change in the method of vacuum break adjustment is required on these models that use the fas t
idle cam " pull-off ' feature . (See Adjustment Procedures
in the 9D-5 Section of the Delco Carburetor Parts an d
Service Manual 9X) .
CHOKE SYSTEM WITH VACUUM BREA K
CLOSING ASSIST SPRIN G
Other 4MV models have the choke closing assis t
9D-5
March 1981
Page 2 1
'
F
Delco
AIR VALVE
SHAFT LEVER
CHOK E
ROD
CHOKE VALVE
S
.0416-
CHOKE CLOSING
ASSIST SPRIN G
FAST IDLE CA M
AIR VALVE
AIR VALV E
DASH-POT ROD
SECONDAR Y
LOCKOUT LEVE R
,,V1
Ili
VACUUM BREA K
ASSEMBL Y
`
FILTE R
SCREEN
r
~t
a4
CHOKE ROD
VACUUM BREAK LEVE R
FAST IDLE
O
00
.4;..
CHOKE COI L
LEVER
UNIT
CHECK BLEE D
VALVE
oar 7
FAST IDLE CAM
FOLLOWER
-
1
NrLOADER TAN G
FAST IDLE SCRE W
THERMOSTATI C
COIL AND RO D
CHOKE SYSTEM
PLASTI C
RETAINER
AIR BLEED
CHOKE SYSTE M
Figure 31 Delayed Vacuum Break Feature
Figure 30 Vacuum Break Closing Assist Sprin g
spring located on the vacuum break plunger stem re placing the torsion spring located on the intermediat e
choke shaft (Figure 30) .
The choke closing assist spring aids in closing th e
choke valve along with tension from the remote choke
thermostatic coil for improved engine starting . The
choke closing assist spring only exerts pressure on th e
vacuum break link to assist in closing the choke valve
during engine starting . When the engine starts and the
choke vacuum break diaphragm seats, the closing spring
retainer hits a stop on the plunger stem and the assis t
spring no longer exerts pressure on the choke valve .
The vacuum break diaphragm plunger is slotted to
allow for free travel of the air valve dashpot link . Th e
slot is moved from the air valve shaft lever to the vacuum
break plunger . A change in air valve dashpot adjustment procedure is required . (See Adjustment Procedures
in the 9D-5 Section, Delco Carburetor Parts and Service
Manual 9X) .
CHOKE SYSTEM WITH DELAYE D
VACUUM BREAK FEATUR E
To delay the choke valve from opening too fast, some
4MV models use a delayed vacuum break system . A n
internal delay valve is included inside the diaphrag m
unit (Figure 31) .
The delay feature operates as follows :
When the engine starts, vacuum acting on the interna l
delay valve bleeds air through a small hole in the valv e
which allows the vacuum diaphragm plunger to mov e
slowly inward . This gives sufficient time to overcome
engine friction and wet the engine manifold to preven t
a lean stall . When the vacuum break diaphragm is full y
seated, which takes a few seconds, the choke valv e
will remain in the vacuum break position until th e
engine begins to warm and relax the thermostatic coi l
located on the exhaust crossover in the intake manifold .
In addition to the internal delay valve, some car
VACUUM BREAK BUCKING SPRING
Figure 32 Vacuum Break Bucking Sprin g
applications have a separate vacuum delay tank adde d
to the system . This is connected "in series " to a secon d
vacuum tube on the vacuum diaphragm unit to further
delay the choke vacuum break diaphragm operation .
The delay valve in the choke vacuum diaphragm uni t
is designed to "pop " off its seat and allow the diaphrag m
plunger to extend outward, when the spring force agains t
the diaphragm is greater than the vacuum pull . Thi s
will give added enrichment as needed on heavy acceleration during cold drive-a-way by allowing the choke coil
to slightly close the choke valve . Some 4MV models
use a calibrated restriction in the vacuum inlet to th e
vacuum break diaphragm unit in place of the interna l
delay valve . Similar to the internal delay valve, the calibrated restriction delays the supply of vacuum to th e
diaphragm unit to retard opening of the choke valve fo r
good engine starting .
CHOKE SYSTEM WITH VACUU M
BUCKING SPRIN G
A spring-loaded plunger is used in the vacuum brea k
unit on some 4MV models (Figure 32) . The purpose of
the spring, called a "bucking spring", is to offset chok e
thermostatic coil tension and balance the opening o f
the choke valve with tension of the choke coil . Thi s
9D-5
March 1981
Page 22
'
F
Delco
enables further refinement of air/fuel mixtures becaus e
the coil, which senses engine and ambient temperatures ,
will allow the choke valve to open gradually against
spring tension in the diaphragm plunger head . In othe r
words, in very cold temperatures, the extra tension
created by the thermostatic coil will overcome the tension of the diaphragm plunger (bucking) spring to
provide less choke valve opening with the result o f
slightly richer mixtures . In warmer temperatures, the
thermostatic coil will have less tension and, consequently ,
will not compress 'the spring as much thereby giving a
greater choke valve opening for slightly leaner mixtures .
PLUNGER BUCKIN G
SPRIN G
THERMOSTATI C
CHOKE COI L
CHOKE SYSTEM WITH DUAL DELAYE D
VACUUM BREAK SYSTE M
Other Quadrajet carburetors use a dual delayed
vacuum break system consisting of front and rear vacuu m
break diaphragm units (Figure 33) .
The dual delayed vacuum break system operates a s
follows :
During engine cranking, the choke valve is held close d
by the tension of the thermostatic coil . This restricts ai r
flow through the carburetor to provide a richer startin g
mixture .
When the engine starts and is running, manifold vacuum is applied to both vacuum break units which ar e
mounted on the side of the float bowl . The front (primary) vacuum break diaphragm opens the choke valve
to a point where the engine will run without loading o r
stalling . As the engine is wetted and friction decreases
after start, a delay valve in the rear (auxiliary) vacuu m
break unit causes a delayed action to gradually ope n
the choke valve a little further until the engine wil l
run at a slightly leaner mixture to prevent loading .
A plunger "bucking spring" may be included on th e
diaphragm plunger of the rear diaphragm unit (Se e
explanation, plunger bucking spring operation) .
A clean air purge feature is added to the rea r
vacuum break diaphragm unit on some 4MV model s
using the dual delayed vacuum break system (Figure 33) .
A clean air bleed, added to the tube at the rear of th e
rear vacuum break unit and located beneath a rubbe r
covered filter, purges the system of any fuel vapor s
and dirt which possibly may enter the internal dela y
valve to disrupt operation . A change in adjustment
procedure for setting the rear vacuum break is require d
on those models using the clean air purge feature . (See
Adjustment Procedures, Section 5, of the Delco Carburetor Parts and Service Manual 9X) .
CHOKE SYSTEM - 4MC (EARLY)
The model 4MC carburetor differs from the 4M V
model in that the thermostatic choke coil is located i n
a choke housing, mounted directly to the side of the
carburetor float bowl, instead of a "remote choke "
coil mounted on the intake or exhaust manifold .
DUAL DELAYED VACUUM BREA K
Figure 33 Dual Delayed Vacuum Break Syste m
CHOKE SHAFT
AND LEVER f'
CHOK E
ROD
I
VACUUM
THERMOSTATI C
COIL
CHOK E
VALV E
- -III
VACUUM BREA K
ADJUSTING SCRE W
VACUUM BREA K
TAN G
EARLY 4MC CHOKE SYSTEM
Figure 34 Early 4MC Choke Syste m
On 4MC models, engine vacuum is supplied throug h
an orifice in the choke housing which pulls heat fro m
the manifold heat stove into the choke housing an d
heat gradually relaxes choke coil tension . This allows
the choke valve to continue opening through inlet ai r
pressure pushing on the offset choke valve and the
weight of the choke linkage pulling the valve open .
On early model 4MC carburetors (Figure 34), th e
vacuum break diaphragm is mounted integrally with th e
choke housing located on the float bowl . An adjustabl e
plastic plunger is included as a part of the vacuu m
break diaphragm . During cold operation after th e
engine starts and is running, manifold vacuum applie d
to the vacuum diaphragm pulls the diaphragm inwar d
and the plunger strikes the vacuum break tang inside
the choke housing which, in turn, rotates the inter mediate choke shaft and through connecting linkage
opens the choke valve to the "vacuum break" position .
CHOKE SYSTEM - 4MC (LATE)
The choke housing on later model 4MC carburetor s
9D-5
March 1981
Page 23
NOTE: PLUNGE R
FRONT VACUU M
BUCKING SPRIN G
CHOKE
BREAK ADJUSTING
USED ON SOME MODEL S
SCREW
/
ROD CHOKE
FRONT VACUUM BREA K
AI R
DIAPHRAG M
VALV E
(DELAY UNIT USED O N
-SOME MODELS )
FRONT VACUU M
BREAK ADJUSTIN G
SCRE W
FRONT VACUU M
BREA K
DIAPHRAGM
CHOKE CLOSING
ASSIST SPRING
THERMOSTATI C
FILTER
PURGE /-DIAPHR AG M SECONDARY
LOCKOU T
FILTER
LEVE R
. rrr~u ~
PURGEL '
FAST IDL E
BLEED
~
CA M
DELA Y
'~
HOLE
VALV E FOLLOWER
INLET
CHECK SPRING
BALL
LATER 4MC CHOKE SYSTEM
~'~~
-
►~
THERMOSTATI C
COIL U
SECONDARY
~\
LOCKOUT FAST IDLE INSIDE FAST IDLE
CAM
CUP ADJUSTIN G
LEVER
PURGE /
FOLLOWER BAFFLE SCRE W
FILTER' ,,,,;
R ~! 1 ~
INLET /rr}•
.- .\ \ DELAY
CHEC K
CHECK
VALVE
BALL
SPRING
FILTE R
TANG
M4MC & M4MCA CHOKE SYSTEM - TYPICA L
Figure 35 Later 4MC Choke Syste m
Figure 36 M4MC-M4MCA Choke System (Typical )
(Figure 35) is also located on the float bowl, but with a
separately mounted vacuum break diaphragm unit .
The vacuum diaphragm unit on some 4MC models includes an internal delay valve for good control of choke
mixtures during the engine warm-up period (see description of Delayed Vacuum Break System, Figure 31) .
Also, a vacuum inlet check ball may be used in th e
vacuum inlet tube on the front and rear vacuum brea k
units . The purpose of the inlet check ball is to preven t
excess dirt and vapor contaminants from plugging th e
small internal delay valve in the diaphragm unit i n
case of engine "backfire " or "dieseling " conditions .
The rear vacuum break unit on some applications
may include a tension (bucking) spring in the diaphrag m
plunger head . (See previous explanation Plunger Buckin g
Spring Operation Page 21) .
CHOKE SYSTEM - M4MC-M4MC A
Similar to 4MC models, an integral choke housin g
and an exhaust heated air thermostatic coil assembl y
are mounted on the carburetor float bowl on M4MCM4MCA models (Figure 36). A single or a dual vacuu m
break system is used for control of choke mixtures durin g
the warm-up period . A special adjusting screw is included on the front vacuum break unit on all "modified"
Quadrajet models . The vacuum break is adjusted by
turning this screw to position a tang on the plunger
that contacts the vacuum break lever .
On some models, the front and/or rear vacuum brea k
units are delayed in operation by an internal delay valve
(see inset, Figure 36) . The valve delays opening of th e
choke valve a few seconds to allow the engine to ru n
on richer mixtures .
A clean air purge feature is used in either the fron t
and rear vacuum break diaphragm units or in the rea r
unit only, depending upon carburetor application, to
prevent dirt from plugging the internal delay valve . A
filter element is installed internally with a small blee d
hole located in the end cover of the diaphragm unit .
During engine operation, vacuum acting upon the diaphragm pulls a small amount of filtered air through th e
bleed hole in the end cover to purge the system of an y
fuel vapors or dirt contamination which might be pulle d
into the internal delay valve located inside the diaphragm
unit . During adjustment of the front and rear vacuu m
breaks, it will be necessary to plug the end cover o f
the vacuum break unit with tape, making sure to sea l
the small bleed hole .
On some M4MC-M4MCA models, the rear vacuu m
break unit includes _a choke closing assist spring (See
Figure 30 and previous explanation of closing assis t
spring operation Page 20) .
Some M4MC-M4MCA models incorporate the "trapped stat" thermostatic coil design whereby the en d
of the thermostatic coil is installed in a slot in the coi l
pick-up lever inside the choke housing . In this way ,
the coil is kept in contact with the pick-up lever at
all times for prompt response to choke coil tension .
FAST IDLE CAM PULL-OFF FEATUR E
A fast idle cam " pull-off ' feature is included on
some M4MC-M4MCA carburetor applications . Manifol d
vacuum to the rear vacuum break diaphragm is supplied
through a water temperature controlled thermal vacuu m
switch (TVS) and by an electrically operated time dela y
solenoid .
During cold operation when manifold vacuum i s
applied through the TVS and the solenoid to the rea r
vacuum break diaphragm, the diaphragm plunge r
moves inward pulling on the vacuum break rod whic h
rotates the vacuum break lever to "pull-off" the fast
idle cam from the high step to the lower step setting .
Thus, the cam "pull-off" feature prevents prolonged
high idle speeds during the warm-up period .
.
9D 5
March 1981
Page 26
is adjusted at the factory . No attempt shoul d
be made to adjust the Idle Load Compensator unless, in diagnosis, curb idle speed i s
not to factory specifications . If adjustment
is necessary, refer to Service Manual for
proper procedure s
MAJOR SERVICE OPERATIONS ALL MODELS
Genera l
The procedures, below, apply to the complete overhaul with the carburetor removed from the engine .
However, in many cases, service adjustments of individual systems may be completed without removing
the carburetor from the engine .
A complete carburetor overhaul includes disassembly ,
thorough cleaning, inspection, replacement of all gaskets — diaphragms — seals — worn or damaged parts ,
and service adjustment of individual systems, plus re storing tamper resistant features where applicable .
Disassembly, Cleaning, Inspection and Adjustment s
The following disassembly and assembly procedures
may vary somewhat between applications due to specifi c
design features . However, they will pertain basicall y
to all Quadrajet models .
AIR HOR N
AIR VALV E
CHOKE
VALVE
PUM P
LEVE R
PUMP
STE M
TYPICAL QUADRAIET CARBURETOR
Figure 42 Typical Quadrajet Carbureto r
Disassembly
NOTICE : Before performing any service o n
the carburetor, it is essential that the carburetor be placed on a holding fixture such a s
BT-30-15 . Without the use of the holdin g
fixture, it is possible to bend or nick throttle valves .
Idle Stop Solenoid Remova l
1. Remove screw(s) securing the idle stop solenoi d
bracket to float bowl and remove solenoid and bracke t
assembly . On some applications, the solenoid an d
bracket assembly are an integral unit and serviced a s
a complete assembly. On some applications where th e
solenoid is mounted in the bracket as a separate unit ,
if solenoid replacement is necessary, bend back retainin g
tabs on lockwasher; then remove large idle stop solenoi d
retaining nut and remove solenoid from bracket .
NOTICE : Follow the above procedure to
remove the A/C idle speed solenoid ,
throttle closing dashpot, or throttle leve r
actuator . The idle stop solenoid, A/C idle
speed solenoid, throttle closing dashpot ,
or throttle lever actuator should not be immersed in any type of carburetor cleane r
and should always be removed before complete carburetor overhaul .
2. On 4MV models using either a Combinatio n
Emission Control (C .E .C .) valve or idle stop solenoi d
mounted on the carburetor :
a) On C .E .C . models only, remove vacuum hos e
from the C .E .C . valve and vacuum tube on the float
bowl .
b) Remove screw securing C .E .C . valve or idle sto p
solenoid bracket to float bowl .
NOTICE : Do not remove the bracket fo r
the C .E .C . valve or idle stop solenoid fro m
the air horn assembly unless replacement o f
the bracket is necessary . If necessary to replace the C .E .C . valve or idle stop solenoid ,
follow procedure noted under Step 1, above .
Do not immerse the C .E .C . valve assembl y
or idle stop solenoid in any type of carburetor cleaner .
AIR HORN REMOVA L
1. If used, remove idle vent valve attaching screw ;
then remove idle vent valve assembly . If thermostatic
vent valve is used, remove dust cover, then remove
valve . Care should be used not to bend or distort th e
bi-metal strip .
2. On those 4MV models using the vacuum operate d
vent switch valve, remove small screw from top of ven t
valve plunger stem .
NOTICE : Hold plunger stem with needle nosed pliers to prevent turning and tearing
of diaphragm . Remove vent valve cover screw
and air horn screw and carefully lift cove r
from air horn . Remove cover gasket, ven t
valve assembly, and spring, noting position
of the vent valve for later reassembly . Re move diaphragm retainer and diaphrag m
from the air horn by carefully moving th e
diaphragm stem back and forth .
41
'
F
9D- 5
March 198 1
Page 2 7
Delco
Figure 43 Removing Upper Choke Leve r
Figure 45 Secondary Metering Rod Remova l
Figure 44 Pump Lever Remova l
3. Remove upper choke lever from the end of choke
shaft by removing retaining screw (Figure 43) . Then ,
rotate lever to remove choke rod from slot in lever .
NOTICE : On models using a clip at the
upper end of the choke rod, remove clip
from rod and disconnect upper end of choke
rod from choke shaft lever .
4. Remove choke rod from lower lever inside th e
float bowl casting .
NOTICE : Remove rod by holding lower lever
outward with small screwdriver and twisting
rod counterclockwise .
5. With tool BT 7523 or equivalent, drive small roll
pin (pump lever pivot pin) inward just enough unti l
pump lever can be removed from air horn (Figure 44) .
Then remove pump lever from pump rod . Note locatio n
of rod (if in inner or outer hole) for later reassembly .
NOTICE : Do not remove roll pin completel y
during removal or disassembly of air horn .
Use care in driving small roll pin to pre -
vent damage to pump lever casting bosse s
in air horn .
On those models that use a retaining clip i n
the upper end of the pump rod, remove clip
from upper end of the pump rod ; then disconnect pump rod from pump lever. Wire
vent valve lever can be removed from pum p
lever if replacement is necessary .
Do not bend the pump rod to remove from
pump lever ; follow the above procedures .
6. Remove secondary metering rods from secondary
orifice plates by removing small screw in the secondary
metering rod hanger (Figure 45) . Lift holder and rod s
as an assembly straight up from the carburetor . Metering
rods may be disassembled from the hanger by rotatin g
ends out of the holes in the end of the hanger .
7. For early models with air valve dashpot, remove en d
of dashpot plunger rod from air valve lever . Some slide
out of lever and others are held by a retaining clip . The
dashpot piston has a synthetic seal inside the piston
on the plunger shaft .
NOTICE : The seal should not be immersed
in carburetor cleaner as the seal will b e
destroyed .
8. Remove air horn to bowl attaching screws (Figure
46) ; early models have 9 screws, later models have 1 3
screws for better control of evaporative emissions . If
used, remove bowl vent valve cover, spring and gasket
from beneath front air horn screw .
9. If used, remove idle vent valve attaching screw ; then
remove idle vent valve assembly . If thermostatic vent
valve is used, remove dust cover, then remove valve .
Care should be used not to bend or distort the bi-meta l
strip .
On those 4MV models using the vacuum operated
vent switch valve, remove small screw from top of ven t
valve plunger stem .
9D.5
March 198 1
Page 28
Figure 46 Air Horn Screw Remova l
NOTICE : Some models have a secondar y
baffle plate mounted under the (2) cente r
air horn attaching screws next to the secondary bores (Nos . 3 and 4) . The baffle ca n
be removed also at this time . Other model s
have a secondary air valve lockout shiel d
located over the lockout lever . This is hel d
in place by the air horn screw next to th e
lockout lever and a small attaching screw .
(Check the "C" parts bulletin in the Delc o
Carburetor Parts and Service Manual 9X fo r
correct usage of these parts) .
10. Remove air horn from float bowl by lifting straight
up (Figure 47) . On 4MV-4MC models, rotate air horn t o
remove vacuum break rod from dashpot lever on end of
the air valve shaft . Air horn gasket should remain o n
bowl for removal later .
NOTICE: Place air horn inverted on clean
bench . When removing air horn from float
bowl, use care to prevent bending the small
tubes protruding from the air horn . These
tubes are permanently pressed into the ai r
horn casting . DO NOT REMOVE .
11. If not removed previously, remove front vacuu m
break hose . Then remove vacuum break control an d
bracket assembly . The diaphragm assembly may no w
be removed from the air valve dashpot rod and the
dashpot rod from the air valve lever .
12. For later models that use a pump plunger ste m
seal (Figure 48), remove seal by inverting air horn an d
use Tool BT-7954 or equivalent to remove seal retaine r
ring . Discard retainer and seal .
NOTICE : Use care in removing the pum p
plunger stem seal retainer to prevent damag e
to air horn casting . A new seal and retaine r
are required for reassembly .
Further disassembly of the air horn is not required for cleaning purposes .
Figure 47 Air Horn Remova l
Figure 48 Pump Plunger Stem Sea l
AIR HORN DISASSEMBL Y
If part replacement is required, proceed as follows :
NOTICE : On "modified" models using th e
bowl vent valve, the bowl vent valve and
actuating arm are permanently retained i n
the air horn . DO NOT REMOVE .
1. Remove staking on (2) choke valve attaching screws ;
then remove choke valve screws, valve, and shaft fro m
air horn .
2. If the air horn is equipped with an air valve lock out lever and it needs replacement, remove the lockou t
lever by driving out roll pin with small drift punch .
NOTICE : Air valves and air valve shaft
should not be removed . However, if it is
necessary to replace the air valve closin g
spring or center plastic eccentric cam, a re pair kit is available . Refer to the "C" Parts
9D- 5
March 198 1
Page 29
L./
FLOAT NEEDL E
PULL CLI P
FLOAT
RETAINING
PIN
FUEL INLET NU T
SAND FILTER
POWER PISTON
AND PRIMARY
METERING ROD S
FLOAT
ASSEMBLY
Figure 49 Pump Remova l
Figure 51 Power Piston Assemblie s
"
~+►"
f '._
ai
AUXILIAR Y
POWER
PISTO N
AUXILIARY POWER PISTON METERIN G
ROD REMOVALL
Figure 50 Auxiliary Power Piston Metering Ro d
Remova l
Bulletin in the Delco Carburetor Parts an d
Service Manual (9X) for part number applica tion .
Instructions for assembly are included in th e
repair kit .
FLOAT BOWL DISASSEMBL Y
1. Carefully lift corner of air horn gasket and remov e
pump plunger from pump well (Figure 49) .
NOTICE : On "modified" models, carefully
loosen air horn gasket and lift one corner t o
remove pump plunger from pump well .
2. If used, remove bowl vent valve spacer from pum p
plunger stem .
3. Remove air horn gasket from dowels on secondary
side of bowl ; then remove gasket from around the mai n
power piston and attached primary metering rods b y
lifting tab of gasket from beneath the hanger (being
careful not to distort the small springs that hold the
metering rods in place) and lift gasket from the bowl .
4. For models that have an auxiliary (front) powe r
piston (as shown in Figure 50), hold auxiliary powe r
piston and swing hanger toward front of carbureto r
while at the same time pushing rearward on meterin g
rod and compressing rod spring retainer until groove i n
rod aligns with slot in hanger . Then remove rod by lifting
it up and out of the fixed metering jet . Hold main (rear)
primary power piston down and swing auxiliary (front )
power piston hanger rearward until it touches the primary power piston — then release the primary pisto n
and remove air horn gasket per step 3 above .
5. Remove pump return spring from pump well .
6. Remove main power piston and metering rods as
an assembly. There are four different types of power pis ton retainers used (Figure 51) .
a. The first design has a "button head" pin extensio n
pressed into the base of the power piston . This typ e
power piston is held in place by the "button head "
which protrudes through a hole in the throttle bod y
gasket. The power piston can be removed by usin g
needle-nosed pliers to pull straight up on metering ro d
hanger directly over power piston .
b. The second type power piston retainer is a fla t
brass spring clip which fits around the power piston ,
at the center . This type power piston assembly is re moved in the same manner as above .
9D- 5
March 1981
Page 30
Delc o
POWER PISTON & METERING RO D
ASSEMBLY-TYPICAL
Figure 52 Power Piston-Metering Rod Assembl y
c. The third type power piston retainer is a spring
clip which fits over and around the top of the powe r
piston cavity . Two fingers at the top of the clip hold the
piston down in the cavity . This type power piston can
be removed by pushing upward on the clip retaine r
to disengage it from the casting .
d. The fourth power piston retainer is a plastic retainer which is part of the power piston assembly . The
plastic retainer fits in a recess at the top of the powe r
piston cavity. The power piston with the plastic retaine r
can be removed by pushing the piston downward against
spring tension and allowing it to snap back against the
retainer . Repeat this snap back action until it "pops "
out of casting . This procedure may have to be repeate d
several times to free the power piston retainer . Do no t
attempt to remove this type power piston by using plier s
on metering rod hanger, as irreparable damage to th e
piston assembly may be caused .
7. Remove metering rods from main power pisto n
hanger by disconnecting tension spring loop from to p
of each rod (Figure 52) ; then, rotate rod to remove fro m
hanger .
NOTICE : Use care when disassembling rod s
to prevent distortion of tension spring and/or
metering rods . Note carefully position of
tension spring for later reassembly .
8. Remove the power piston spring(s) from the well .
9. If used, remove auxiliary (front) power pisto n
by depressing piston stem and allowing it to snap free
(following procedure noted in Step 6d, above) . Remov e
auxiliary power piston spring from the well .
NOTICE : The main (rear) and auxiliary
(front) power piston springs must NOT be
interchanged . To prevent mixing of springs ,
lightly wrap a piece of masking tape aroun d
the auxiliary power piston spring for identification . The auxiliary (front) power pisto n
spring is the longer of the two springs .
10 . Remove plastic filler block over float valve .
11 . Remove float assembly and float needle by pullin g
up on hinge pin .
12 . Remove inlet needle seat and gasket using Too l
BT-3006M or wide blade screwdriver .
NOTICE : Float needle and seat are factory
matched and tested and should be replace d
only as a set .
For diaphragm type float assemblies (earl y
models) :
a. Remove float assembly by pulling upward on hing e
pin until pin can be removed from float hanger b y
sliding toward pump well . After pin is removed, slide
float assembly toward front of bowl to disengage needl e
pull clip from float arm . Do not distort float needl e
pull clip .
b. Using needle-nosed pliers, remove pull clip fro m
float needle .
c. Remove two screws from float needle diaphrag m
retainer ; then remove retainer and float valve assembl y
from bowl .
NOTICE : Valve seat is factory staked and
tested. Do not attempt to remove or restake .
If damaged, replace float bowl assembly .
APT METERING ROD - WIT H
ANEROID OR FILLER SPOO L
13 . On later "modified " models that use the AP T
(adjustable part throttle) metering rod assembly with
aneroid or filler spool, remove two cover screws and
carefully lift the metering rod assembly from the floa t
bowl cavity (Figure 53) .
NOTICE : The APT metering rod assembly ,
with aneroid or filler spool, is extremely
fragile . Use care in handling these critical
parts . Do not immerse aneroid or filler spoo l
in carburetor cleaner . The APT metering ro d
assembly is pre-set at the factory and N O
attempt should be made to readjust in th e
field . If replacement is necessary, see APT
Metering Rod Replacement (Step 7a ,
page 38) .
14 . Many models have a simple blank insert installe d
in the aneroid bowl cavity (Figure 53) . Remove insert .
9D- 5
March 198 1
Page 31
'
F
Delco
TYPICAL (`MODIFIED') FLOAT BOWL
Figure 54 M4MC-M4ME "Modified" Float Bowl Typica l
Figure 53 Modified APT Devices
NOTICE: On M4MC-M4ME models that
have an APT Metering Rod Adjustmen t
screw in the float bowl (located in a wel l
next to the main power piston), the scre w
is pre-set at the factory and no attemp t
should be made to change this adjustment
in Service . If float bowl replacement is
required for service, the new bowl assembl y
will be supplied with the APT meterin g
screw pre-set as required .
15. Remove main metering jets only if necessar y
(Figure 54) .
NOTICE : No attempt should be made to re move the auxiliary (front) power pisto n
metering jet, APT metering jet, or secondary
metering orifice plates . Normal cleaning i s
all that is necessary . These jets are fixed and,
if damaged, float bowl replacement is required .
16. Using a screwdriver, remove pump discharg e
check ball retainer, then steel check ball (Figure 54) .
17. If used, remove baffle from side of pump wel l
fill slot .
18. The baffle plate in the secondary bores need not
be removed for cleaning purposes . If replacement is
necessary, remove plate by lifting upward out of slot s
in side of bores .
19. CHOKE MECHANISM DISASSEMBL Y
A . Vacuum Break Remova l
1 . Remove vacuum break hose from main vacuu m
break assembly and, if used, from rear (or auxiliary)
Figure 55 Vacuum Break and Fas t
Idle Cam - Early Model s
vacuum break assembly, and remove hose(s) from connection on float bowl .
2. Remove retaining screw from choke vacuum break
bracket assembly and remove assembly from float bowl .
If not removed previously, vacuum break rod can no w
be removed from the main vacuum break plunger b y
rotating rod out of plunger stem (Figure 55) .
3. Remove secondary lockout lever, or idle speed-u p
lever (where used), from projection on bowl casting .
4. Remove the fast idle cam from bushing on choke
vacuum break bracket assembly .
NOTICE : If further disassembly of the chok e
9D- 5
March 198 1
Page 32
Delc o
Figure 57 Choke Housing Remova l
Figure 56 Secondary Vacuum Break Remova l
mechanism is necessary, the vacuum brea k
assemblies can be removed as follows :
. a) (Early Models) Remove clip on connecting link a t
vacuum break lever . Then, remove link from lever an d
vacuum break diaphragm plunger .
b) Some models have vacuum break units attache d
to the brackets by retaining ears which are bent togethe r
to hold the diaphragm assembly . Where found, the retaining ears must be spread to unclamp either the primary (front) or secondary (rear) vacuum break assembly .
c) Late models have integral vacuum break diaphragm bracket assemblies . Remove attaching screws holding
units to float bowl . The secondary vacuum break assembly has a rod connecting the plunger to the intermediate
choke shaft lever . This can also be removed by rotating
the vacuum break diaphragm assembly by sliding th e
rod out of the plunger stem and the other end out of
the vacuum break lever (See Figure 56) .
NOTICE : Do not place vacuum break unit s
in carburetor cleaner .
B . Choke Disassembly (Early Models )
1. Remove three attaching screws and retainers from
choke cover and coil assembly . Then pull straight out ward to remove cover and coil assembly from chok e
housing . Remove choke cover gasket if used .
NOTICE : A cover scribe mark is locate d
relative to the index marks cast into th e
choke housing . The cover position should b e
noted at time of disassembly so that cove r
indexing can be restored upon reassembly .
NOTICE : It is not necessary to remove baffle
plate from beneath the thermostatic coil o n
hot air choke models . Distortion of th e
thermostatic coil may result if forced off th e
center retaining post on the choke cover .
2. Remove choke housing assembly from float bowl
by removing retaining screw and washer inside the choke
housing (Figure 57) . The complete choke assembl y
can be removed from the float bowl by sliding outward .
3. Remove lower choke lever from inside float bowl
cavity by inverting bowl .
4. Remove plastic tube seal from choke housing i f
used .
NOTICE : Plastic tube seal should not b e
immersed in carburetor cleaner .
5. To disassemble intermediate choke shaft from
choke housing, remove coil lever retainer screw . The n
remove lever from flats on intermediate choke shaft .
Remove intermediate shaft from the choke housing b y
sliding outward . The fast idle cam can now be removed
from the intermediate choke shaft .
6. Remove the cup seal from inside choke housin g
shaft hole if the housing is to be immersed in carburetor cleaner . Also, remove cup seal from the floa t
bowl insert for bowl cleaning purposes (Figure 58) .
NOTICE : Do not attempt to remove bowl
insert .
C . Choke Disassembly (Late Models )
Late model carburetors have a tamper resistant chok e
cover locating and retention method . Cover and coi l
assembly retainer screws (early models) have been re placed by rivets to discourage choke readjustment i n
the field . Should it be necessary to remove the cove r
and coil assembly or choke housing for cleaning, over haul or replacement, proceed as follows :
CHOKE COVER REMOVA L
1. Support float bowl and throttle body as an assembl y
on a suitable holding fixture such as tool BT-30-15 .
2. Carefully align a #21 drill ( .159") on rivet hea d
and drill enough to remove the three rivet heads (Figur e
59) and then, using a drift and small hammer, driv e
the remainder of the rivets out of the choke housing .
'
F
9D-5
March 198 1
Page 3 3
Delco
SEAL INTERMEDIATE
CHOKE SHAF T
IN FLOAT BOW L
LEVER - SECONDAR Y
LOCKOU T
(OUADRAJET ONLY)
SEAL - INTERMEDIATE CHOKE
SHAFT IN CHOKE HOUSIN G
(HOT AIR CHOKES ONLY )
(2) screws in compensator cover at rear of float bowl .
Remove cover, hot idle compensator, and "0" ring
seal in bowl cavity recess beneath compensator .
Some models have the hot idle compensator located ad jacent to the pump well area . Remove hot idle compensator assembly and cork "0" ring .
NOTICE: Hot idle compensator "0" ring
seal is to be replaced with a new seal at
time of reassembly.
2. Remove fuel inlet nut, gasket, filter assembly an d
spring (Figure 60) . Some models use a fuel strainer i n
place of a filter and spring . Consult the parts list for
each model for proper parts application .
3. Invert float bowl - throttle body assembly and plac e
on a clean flat surface . Remove throttle body by re moving throttle body to bowl attaching screws (Figur e
61) . Lift throttle body from bowl .
4. Remove throttle body to bowl insulator gasket .
SCREW - CHOK E
HOUSING ATTAC H
Figure 58 Choke Assembly - Typica l
Figure 60 Fuel Filter Assembly - Typica l
Figure 59 Choke Cover Removal - Late Models
NOTICE : On tamper resistant models a
special cut-out is notched in the choke cove r
which is aligned with an extended tab on
one cover retainer which is located at the
2 o'clock position . This is a locating method
that properly indexes the cover and coil
assembly within the choke housing .
3. Remove choke cover and coil assembly from chok e
housing . Remove choke cover gasket, if used ; also remove inside baffle plate, if used .
4. Remove choke housing assembly from float bowl
using procedures described previously for early models .
DISASSEMBLY OF REMAININ G
FLOAT BOWL PART S
1 . If used, remove hot idle compensator by removing
Figure 61 Throttle Body Remova l
9D•5
March 198 1
Page 34
THROTTLE BODY DISASSEMBLY
NOTICE : Place throttle body assembly
on carburetor holding fixture to protect
throttle valves . Extreme care must be taken
to avoid damaging throttle valves .
1. Remove pump rod from throttle lever by rotating
rod out of primary throttle lever .
2. Further disassembly of the throttle body is no t
required for cleaning purposes . The throttle valve screws
are permanently staked in place and should not b e
removed . The throttle body is serviced as a complet e
assembly .
NOTICE: Do not remove the steel plugs that
cover the idle mixture needles (late models )
or the plastic limiter caps that are found o n
some models . These devices are installed to
protect critical factory settings and to meet
emissions control regulations . If proble m
diagnosis indicates that the carburetor is at
fault relative to a driver complaint, an emissions failure, or if normal soaking and ai r
pressure fails to clean the idle passages, or
if idle needle or throttle body replacement is
required, only then may the plugs or limiter
caps be removed in order to perform necessary
service .
If plug removal is required to replace idle needle s
or to perform necessary adjustments, proceed as follow s
(Figure 62) :
a. Make two parallel cuts in the throttle body betwee n
the locator points beneath the idle mixture needle plugs
with a hack saw (Step 1) . The cuts should reac h
down to the steel plug but should not extend more tha n
1/8" beyond the locator points . The distance betwee n
the saw marks depends on the size of the punch t o
be used .
b. Place a flat punch at a point near the ends of the
saw marks in the throttle body . Holding the punch at a
45° angle, drive it into the throttle body until the casting breaks away, exposing the steel plug (Step 2).
c. Holding a center punch vertical, drive it into the
steel plug. Then, holding the punch at a 45° angle ,
drive the plug out of the casting.
NOTICE: Hardened plug will break rathe r
than remaining intact . It is not necessary
to remove the plug completely ; instead ,
remove loose pieces to allow use of idle mixture adjusting tool J-29030 or BT-7610B (o r
equivalent) .
d. Using Tool J-29030, or BT-7610B, adjust idle
mixture needle according to specifications . If the idle
mixture needles are removed, readjust the idle mixtur e
per recommended instructions furnished by the vehicl e
manufacturer or provided in AC-Delco Service Bulletins
SD-100, SD100A or 9D-1978A .
Figure 62 Idle Mixture Plug Remova l
NOTICE: Before removing the idle mixture
needle, it is suggested that the old needle b e
lightly bottomed and the number of turns to
bottom be recorded . Then, when installing
the new needle, lightly bottom, then bac k
off the number of turns it took to bottom
the old needle . Proceed to adjust needles t o
final idle mixture following procedures an d
specifications.
NOTICE: After idle mixture adjustment is
complete on models where plugs were re moved, it is advised that the needle settings
be sealed with a silicone sealant RTV rubber
or equivalent to prevent fuel vapor loss . If
necessary to remove the idle mixture needle s
with idle limiter caps, destroy the limite r
caps . Do not install a replacement cap as a
bare mixture screw is sufficient evidence to
indicate that the mixture has been readjusted .
CLEANING AND INSPECTIO N
1. Thoroughly clean carburetor castings and meta l
parts in an approved carburetor cleaner, such as Carbo n
X (X-55) or its equivalent .
NOTICE: The following should NOT b e
immersed in carburetor cleaner as they wil l
swell, harden, or distort :
A. The electric choke, any rubber parts, electric
solenoid, plastic parts, diaphragms, pump plunger ,
aneroid, filler spool, or aneroid cavity inser t
B. Vacuum Break Assemblie s
C. Choke housing plastic tube seal or gasket
D. Choke coil and cover assembl y
E. Intermediate choke lever shaft cup seal recesse d
in float bowl insert
9D- 5
March 198 1
Page 3 5
F. If choke housing is to be immersed in carbureto r
cleaner, remove the cup seal from inside the chok e
housing shaft hole
G. Fuel filter assembly, and check valve (if used )
H. Idle stop solenoid, A/C idle speed solenoid ,
throttle closing dashpot, throttle lever actuator, C .E.C .
solenoid .
The plastic cam on the air valve shaft will withstan d
normal cleaning in carburetor cleaner (rinse thoroughl y
after cleaning) .
Do not attempt to remove bowl insert . The bushing
will withstand normal cleaning . (Rinse thoroughly after
cleaning) .
2. Thoroughly clean all metal parts and blow dry wit h
shop air. Make sure all fuel passages and metering
parts are free of burrs and dirt . Do not pass drills or
wire through jets and passages .
3. Inspect upper and lower surface of carbureto r
castings for damage.
4. Inspect holes in levers for excessive wear or out of
round conditions . If worn, levers should be replaced .
5. Check, repair, or replace parts if the followin g
problems are encountered :
A . Flooding
1. Inspect float needle and seat for dirt, deep wear
grooves, scores, and proper seating . (Needle and seat
checking tool BT-6513 may be used to check the sea l
of the standard type needle in the seat) .
NOTICE : When checking the rubber tipped
needle, do not exceed 3" of vacuum for six
seconds to prevent distortion of the rubber tip .
2. Inspect float needle pull clip for proper installation .
Be careful not to bend needle pull clip .
3. Inspect float, float arms and hinge pin for distortion, binds, and burrs . Check density of material i n
the float ; if heavier than normal, replace float .
4. Clean or replace fuel inlet strainer or filter .
B . Hesitatio n
1. Inspect pump plunger for cracks, scores, or excessive cup wear .
2. Inspect pump duration and return springs for bein g
weak or distorted .
3. Check all pump passages and jets for dirt, improper seating inlet or discharge balls, scores in pum p
well .
4. Check pump linkage for excessive wear, repair
or replace as necessary .
C . Hard Starting-Poor Cold Operatio n
1. Inspect inlet needle for sticking, dirt, etc .
2. Examine fast idle cam for wear or damage .
3. Also check items under "Flooding" .
D . Poor Performance - Poor Gas Mileag e
1. Clean all fuel and vacuum passages in castings .
2. Check choke valve for freedom of movement .
3. Inspect power piston(s), metering rods and jets fo r
dirt, sticking, binding, damaged parts or excessive wear .
4. Check air valve for binding condition . If air valve
is damaged, the air horn assembly must be replaced .
A torsion spring kit is available for repairs to the ai r
valve closing spring . A new plastic eccentric cam is
included in the kit .
E . Rough Idl e
1. Inspect gasket mating surfaces on castings fo r
damage to sealing beads, nicks or burrs .
2. Clean all idle fuel passages.
3. Check throttle lever and valves for binds, nicks
and other damage .
4. If removed, inspect mixture needles for ridges, burrs ,
or being bent . Install idle mixture needles and spring s
until needles are lightly seated . Back out mixture needles
specified number of turns as an initial adjustment .
NOTICE : Final idle mixture and idle spee d
settings should be made on the car followin g
the vehicle manufacturer's procedures and
specifications noted in the service manual or
AC-Delco Service Bulletins SD-100, SD-100A ,
or 9D-1978A .
5. Check all diaphragms for possible ruptures or leaks .
6. Clean plastic parts only in cleaning solvent - neve r
in gasoline .
CARBURETOR ASSEMBL Y
Throttle Body Reassembly
1. If removed, install fast idle cam follower, fast idl e
lever on end of primary throttle shaft . Install torsio n
spring (where used) and retaining screw in end of shaft .
Tighten securely.
2. If removed, install idle mixture needles and spring s
until lightly seated . Then, as a preliminary idle mixture
adjustment, back out the mixture needles number o f
turns counted at time of disassembly (see step 2, Pag e
34), or back out mixture needles number of turns specified by the vehicle manufacturer . Final adjustment
must be made on the engine using the procedures and
specifications of the vehicle manufacturer .
NOTICE : Do not force the idle mixture
needle against the seat or damage will result .
3. Install lower end of pump rod in throttle lever
by aligning tang on rod with slot in lever . End of ro d
should point outward toward throttle lever .
9D-5
March 198 1
Page 38
'
F
Delco
Float Bowl Reassembly (Refer to Figures 49 through 60 )
1. Install new throttle body to bowl insulator gaske t
making sure the gasket is properly positioned on tw o
locating dowels on bottom of float bowl .
2. Install throttle body on bowl making certain throttle
body is properly located over dowels on float bowl ;
then install throttle body to bowl screws (and lockwashers,
if used) and tighten evenly and securely .
NOTICE : If a new (service) throttle body is
used on 4MV-4MC models, be sure to per form APT setting procedures as described
on page 42 . Place carburetor on prope r
holding fixture (such as BT-30-15) .
3. Install fuel inlet strainer, or filter (and check valve ,
if used), spring, new gasket and inlet nut . Tighten
nut securely (18 ft. lbs .). The filter spring is not use d
on models that have a fuel strainer .
NOTICE : When installing a service replacement filter, make sure the filter is the type
that includes the check valve, if required, t o
meet government safety standards . New service replacement filters with check valve meet
this requirement . When properly installed ,
hole in filter faces toward inlet nut . Ribs o n
closed end of filter element prevent filte r
from being installed incorrectly unless forced .
Tightening beyond specified torque ca n
damage nylon gasket.
4. If used, install hot idle compensator "0" ring
seal in recess in bowl, then install hot idle compensator .
Install compensator cover and (2) retaining screws .
Tighten screws securely.
NOTICE : On those models having the compensator located in the float bowl adjacen t
to the pump well area, install "0" ring
cork seal and hot idle compensator in cavit y
in float bowl .
4MV Choke Assembl y
5. If the vacuum break diaphragm (s) was remove d
from the bracket, slide vacuum break diaphragm between retaining ears and bend ears down slightly t o
hold securely . .
NOTICE : If a second (auxiliary) vacuu m
break diaphragm is used, the vacuum diaphragm rod must be installed in the vacuu m
break lever and plunger stem prior t o
installing the unit on the choke bracket .
Models
Install vacuum break link (U-bend end) in slot in
diaphragm plunger . End of link should be on insid e
of slot toward choke bracket . Install other end of vacuum
beak link in hole on vacuum break lever and retai n
with clip .
Early
6. Install the secondary lockout lever (or idle speed up lever, if used,) on the bearing pin on the float bowl .
7. Install fast idle cam on the choke shaft making
sure the cam actuating tang on the intermediate choke
shaft lever is located on the underside of the tail o f
the fast idle cam, or in slot of fast idle cam .
Assembly of Choke Housing to Float Bowl
1. If used, install new cup seal into insert on sid e
of float bowl for intermediate choke shaft . Lip on cu p
seal faces outward .
2. Install secondary throttle valve lockout lever (i f
used) on boss on float bowl with recess in hole i n
lever facing inward (Figure 63) .
Figure 63 Assembly of Choke Housing to Floa t
Bow l
3. If used, install new cup seal into inside choke
housing shaft hole . Lip on seal faces inward, towar d
float bowl .
4. Install fast idle cam onto the intermediate choke
shaft (steps on fast idle cam face downward) .
5. Except on early 4MC models, carefully install fas t
idle cam and intermediate choke shaft assembly throug h
seal in choke housing; then install thermostatic coil
lever onto flats on intermediate choke shaft . The thermostatic choke coil lever is properly aligned when bot h
inside and outside levers face toward fuel inlet . Install
inside lever retaining screw into end of intermediate
choke shaft . Tighten screw securely.
6. Install choke rod (plain end) into hole in lowe r
choke rod inner lever; then holding choke rod wit h
lower end pointing outward, lower choke rod inne r
lever into cavity in float bowl . Install plastic tube seal
(if used) into cavity on choke housing before assemblin g
choke housing to bowl . On early 4MC models with
vacuum diaphragm unit integral with choke housing ,
install small gasket on vacuum passage between choke
9D• 5
March 198 1
Page 3 7
'
F
Delco
housing and float bowl . Install choke housing to bow l
sliding intermediate choke shaft into lower choke inne r
lever .
NOTICE: Tool BT-6911 can be used to hol d
the lower choke rod inner lever in correc t
position while installing the choke housing
as shown in Figure 64 .
.
Install
choke housing retaining screw and washer
7
and tighten securely .
NOTICE : The intermediate choke shaft leve r
and fast idle cam are in correct relatio n
when the tang on lever is beneath the fast
idle cam . Do not install choke cover and coil
assembly until inside coil lever is adjusted
(see Adjustment Procedures Bulletin 9D-5 A
of the Delco Parts and Service Manual 9X) .
3. If removed, install baffle in secondary side o f
float bowl with notches toward top of bowl . Make sure
baffle is seated and top is flush with casting surface .
4. On M4MC-M4ME models, install baffle insid e
pump well with slot toward bottom .
5. Install pump discharge ball and retainer in passage
next to pump well . Tighten retainer securely .
6. Install primary main metering jets, if removed .
TIGHTEN SECURELY .
7. On "modified" models that use an APT meterin g
rod assembly with aneroid or filler spool, install metering
rod assembly into float bowl, carefully aligning meterin g
rod tip with hole in fixed jet . Tab on cover goes in slot
in float bowl closest to the fuel inlet nut (Figure 66) .
TYPICAL ('MODIFIED') FLOAT BOW L
Figure 65 Float Bowl - Typica l
Figure 64 Installing Lower Choke Rod Lever
COMPLETION OF FLOAT BOW L
ASSEMBLY - ALL MODELS
NOTICE : Steps 1 and 2 pertain only to
M4MC-M4ME units that use a rear vacuu m
break assembly .
1. Holding down on fast idle cam (hot idle position) ,
install end of rear vacuum break rod in hole in inter mediate choke lever .
2. Install end of vacuum break rod in slot in rea r
vacuum break plunger . Then install rear vacuum brea k
and bracket assembly to float bowl using two attachin g
screws . Tighten securely .
NOTICE: Do not attach vacuum break hose
until after the rear vacuum break adjustment is completed .
Figure 66 APT Metering Rod Replacemen t
9D-5
March 198 1
Page 3 8
NOTICE: The position of the APT meterin g
rod, with aneroid or filler spool, in the fixe d
jet is extremely critical . Adjustment shoul d
NEVER be attempted unless replacement o f
the APT metering rod assembly is require d
due to damage to the rod, or failure of th e
original aneroid .
If required, the threaded metering rod assembl y
may be replaced as follows :
a. Note position of slot in adjusting screw of metering
rod assembly and lightly scribe mark on cover .
b. With cover screws removed, carefully lift th e
metering rod and cover assembly from the float bowl .
NOTICE : DO NOT immerse the aneroid or
filler spool in carburetor cleaner . The metering rod assembly, with aneroid or filler spool ,
is extremely fragile . Use care in handlin g
these critical parts .
c. With metering rod and cover assembly held up right, using a small screwdriver, turn the adjusting
screw counterclockwise, carefully counting the number
of turns until the threaded metering rod assembly bottoms in the cover. Record number of turns counte d
for later reference (see Step f) .
d. Remove "E" clip retainer from threaded end of
rod . Then using small screwdriver, turn slotted rod clock wise until rod assembly disengages from cover .
NOTICE : Rod assembly is spring-loaded .
Use care in removing rod assembly from cover.
e. Install tension spring on replacement metering rod
assembly and thread rod and spring assembly int o
cover until the rod assembly bottoms in cover .
f. Using a small screwdriver, turn the adjustin g
screw clockwise until the rod is backed out of the cover
exactly the same number of turns from scribe line as
recorded during disassembly (see Step c) .
NOTICE: When properly adjusted as above ,
slot in replacement AFT metering rod assembly may not line up with scribe mark on cover .
g. Install "E" clip in groove in rod assembly, makin g
sure clip is locked securely in place .
h. Carefully install cover and metering rod assembl y
onto float bowl aligning tab on cover assembly wit h
slot in float bowl closest to the fuel inlet nut, (Figure 66) .
NOTICE: Use care installing the metering
rod and cover assembly into float bowl t o
prevent damaging or bending the meterin g
rod tip.
i. Install cover attaching screws and tighten securely .
8. On other "modified" models that do not use th e
APT metering rod assembly with aneroid or filler spool ,
install aneroid cavity insert into float bowl .
Figure 67 Float Needle Pull Clip Locatio n
9. Install needle seat, with gasket, using tool BT3006M .
10. To make float adjustment easier, carefully ben d
float arm upward at notch in arm before assembly .
11. Install needle by sliding float lever under pul l
clip from front to back . Correct installation of the needl e
pull clip is to hook the clip over edge of the float on the
float arm facing the float pontoon (Figure 67) . With
float lever in pull clip, hold float assembly at toe an d
install hinge pin from pump well side (ends of hing e
pin face the accelerating pump well) .
NOTICE : Do not install float needle pul l
clip into holes in float arm . Severe flooding
will result.
12. Install float needle and diaphragm assembly ,
making sure diaphragm is properly seated .
13. Install diaphragm retainer and two screws . Tighten
securely.
14. Install float needle pull clip on float needle stem
using needle nosed pliers. Pull clip is properly positioned
with open end toward front of bowl .
15. Install float by sliding float lever into loop in
pull clip . With lever in clip, hold float assembly a t
toe and install float hinge pin from pump well side .
Be careful not to bend needle pull clip .
NOTICE : If desired, certain Quadrajet
models may be converted from the diaphrag m
type needle and seat to the standard or conventional float needle and seat by installing
a service modification kit . (Refer to 9C Parts
Section of the Delco 9X Manual for specifi c
applications and part number )
16. Carefully adjust float level following procedures
and specifications listed in the vehicle manufacturer 's
service manual or in the "D" section of the Delco Carburetor Parts and Service Manual (9X) .
'
F
9D-5
March 198 1
Page 39
Delco
17. On M4MC-M4ME models, install plastic fille r
block over float needle, pressing downward until properl y
seated .
18. Install power piston spring in power piston well .
NOTICE : If two power piston springs are
used, the smaller spring seats in the cente r
of the piston and bottoms on the float bow l
casting . The larger diameter spring surround s
the small inner spring to exert additiona l
pressure on the bottom of the power piston .
19. If primary metering rods were removed fro m
hanger, reinstall making sure tension spring is connecte d
to top of each rod (see Figures 52 or 68) .
20. Install power piston assembly in well with meterin g
.rods carefully positioned in metering jets .
NOTICE :
a) On those models that have a "Butto n
Head" pin extension pressed into the bas e
of the power piston, press down firmly t o
insure engagement of retaining pin in throttle
body gasket.
b) Some models use a spring clip over top of
power piston well . On these, make sure clip
is installed and seated .
c) On those which have a split ring retainer
around the center of the power piston, carefully compress split ring and push pisto n
down in well until it seats . This properly
positions this type retainer .
On late models which use the plastic retainer on the top of the power piston (a s
shown Figure 68),install power piston in wel l
and press down firmly on the plastic retainer
forcing it into the recess in the bowl . Make
sure it is properly seated . It may be necessary
to tap the plastic retainer lightly in plac e
with a hammer and drift . When installe d
correctly the plastic retainer is flush with the
top of the float bowl casting .
21. On "modified" models with dual power pistons ,
remove masking tape, used for identification, and install
auxiliary power piston spring in power piston well (fron t
location — long spring) .
Install auxiliary power piston assembly without metering rod in front well . Press down firmly on plastic power
piston retainer to make sure the retainer is seated i n
recess in bowl and that the top is flush with the top o f
the float bowl casting . If necessary, using a drift punch
and small hammer, tap retainer lightly in place .
22 . On 4MV-4MC models, install plastic filler block
over float needle, pressing downward until properl y
seated.
23 . Install accelerator pump return spring in pump
well .
Figure 68 Power Piston Installatio n
24. On dual power piston models, hold main (rear )
power piston down and swing auxiliary (front) powe r
piston rearward until it touches the main power piston.
Then release main power piston .
25. Install air horn gasket by carefully sliding tab o f
gasket around metering rods and beneath the power
piston hanger . Position gasket over the two dowel pin s
on the float bowl .
NOTICE : Air horn gaskets for "modified"
Quadrajet models differ in that some hav e
an extra hole forward of the main meterin g
rod hanger, either for the auxiliary hange r
(dual power piston models) or for the AP T
adjustment screw (Fig . 69) . Be sure to use
the correct gasket for the carburetor being
worked on.
26. On dual power piston models, hold main (rear)
power piston down and swing auxiliary power piston
toward front of carburetor . Release main power piston .
Holding auxiliary power piston down with hange r
toward front of carburetor, carefully insert the auxiliary
metering rod in the fixed jet . Using finger to compres s
spring toward end of rod, slide rod onto small diamete r
groove in hanger and release spring . Correct spring
location is on front side of hanger facing fuel inlet nut
(Fig. 50) . The hanger, when properly installed, will
point toward rear of the metering rod cover (with aneroid
or filler spool) .
27. 4MV-4MC models — install accelerator pump
plunger in pump well . M4MC-M4ME models — if used,
install bowl vent valve spacer on accelerator pum p
plunger stem . Carefully lift corner of the air horn
gasket and install accelerator pump plunger in the pump
well by pushing the plunger to the bottom of the wel l
against return spring force . While holding in thi s
position, align pump plunger stem with hole in gasket
and press gasket into place (Figure 69) .
.
9D 5
March 198 1
Page 40
'
F
DelC O
enrichment tubes (if used), and accelerating well tube s
with proper holes hi gasket, and positioning pump plunge r
stem through hole in air horn.
On 4MV models using a "clipless" vacuum break
rod, install vacuum break rod into main (front) vacuu m
break diaphragm plunger and into air valve lever on
air horn before the air horn is lowered onto the floa t
bowl .
Position pump plunger stem in air horn and dashpot
(where used) in well in float bowl . Gently lower ai r
horn assembly on gasket on float bowl, locating dowel s
through gasket until properly seated.
Figure 69 Installing Air Horn
AIR HORN REASSEMBL Y
1 . Install the following, if removed :
a) Pump stem seal and retainer .
b) Choke shaft, choke valve and (2) attaching screws .
Tighten screws securely in place .
c) Dashpot plunger rod through air horn and attache d
to air valve dashpot lever . Make sure clip retainer is
installed (where used) .
d) Air valve lockout lever (if used) - retain with roll
pin . Make sure lever is free from binds .
e) Normally, the air valve and shaft do not have to
be removed from the air horn for cleaning purposes . A
repair kit is available which includes a new plastic cam ,
an air valve torsion spring, and retaining pin . Complet e
instructions for installation also are included in the kit .
(Refer to the C Parts Bulletin in the Delco Carburetor Parts and Service Manual for part number application) .
If it was necessary to replace the air valve closin g
spring and the air valve shaft was removed, install ai r
valve shaft, plastic cam, air valves and four (4) attaching
screws . Center air valves, tighten screws and stake in
place . Make sure air valve operates freely with no binds .
Then install air valve closing spring in air horn cavity .
Insert spring pin, adjust pin, adjust air valve closing
spring as outlined under adjustment procedures .
""
AIR HORN TO BOWL INSTALLATIO N
1 . 4MV-4MC models - Carefully lower air horn assembly onto float bowl, aligning bleed tubes, pull-over
2. M4MC-M4ME Model s
Carefully lower air horn assembly onto float bow l
(holding down on air horn gasket at pump plunger
location), making sure that the bleed tubes, pull-ove r
enrichment tubes (if used), and pump plunger stem are
positioned properly through the holes in the air horn
gasket (Figure 69) .
NOTICE : ALL MODELS — DO NOT
FORCE THE AIR HORN ASSEMBLY
ONTO THE BOWL, BUT RATHER LIGHTLY LOWER IN PLACE . IF AIR HORN
DOES NOT SEAT EASILY, CHECK ALIGN MENT OF AUXILIARY METERING RO D
HANGER (IF USED) .
3. Install air horn to float bowl attaching screws .
(Early models have (9), late models have (13), see Figure
70) . The (2) long screws go through the secondary side of
the air horn at rear and (2) countersunk screws go inside
primary bores next to venturi . Install air valve lockou t
guard (if used) under intermediate length screw (#4 in
Figure 70) and secure with self-tapping screw . If used ,
install air horn baffle (secondary side) beneath #3 and
#4 air horn screws . Air horn screws (except countersunk screws) may or may not use lockwashers dependen t
upon application. Tighten all screws evenly and securely
(see Figure 70 for proper tightening sequence) .
NOTICE : Do not install air horn screw #5
on M4MC-M4ME models using a bowl vent
valve until completion of bowl vent valv e
adjustment . Then, install bowl vent valve
spring, gasket, and cover, retaining with # 5
air horn screw . On 4MV models using th e
vacuum operated vent switch valve, do not
install #5 air horn screw until valve cover is
installed (see Step 7, Page 41) .
4. On 4MC-M4MC-M4ME models, install fron t
vacuum diaphragm rod into the slot in lever on the en d
of the air valve shaft . Then, install other end of ro d
into hole in the front vacuum break diaphragm plunger .
Install front vacuum break diaphragm and bracket assembly to float bowl (4MC) or air horn (M4MC-M4ME )
and retain with two screws . Tighten screws securely.
'41
9D.5
March 1981
Page 4 1
Figure 70 Air Horn Screw Tightening Sequenc e
NOTICE: Do not attach vacuum break hose
until vacuum break adjustment is completed .
5. 4MV Models - Connect choke rod into lower chok e
lever inside bowl cavity. Then install upper end of rod
into upper choke lever and retain rod in upper leve r
with clip .
making sure diaphragm is not wrinkled or torn . Lightly
tap diaphragm retainer into air horn assembly until fully
seated . Install diaphragm spring over diaphragm ste m
and, with stem raised, compress spring while sliding
vent valve assembly under slot in diaphragm stem .
NOTICE : Part number and " RP" on vent
valve face upward . Install vent valve cover
gasket, cover, and screw . Align cover with
holes in air horn and tighten screw securely .
Install longer air horn screw in vent valv e
cover and air horn and tighten screw securely .
Install pump override lever on diaphragm
stem and retain with small screw . Tighte n
screw securely .
8. Install (2) secondary metering rods into the secondary metering rod holder (upper ends of rods point
toward each other) . Install secondary metering rod holder
(with rods positioned in secondary metering discs) ont o
air valve cam follower . Install retaining screw and tighte n
securely . Work air valves up and down several time s
to make sure they are free in all positions .
9. Connect upper end of pump rod to pump lever . I f
two hole pump lever is used, make sure pump rod is in
specified hole in lever, noted at disassembly (or se e
specifications) . Place pump lever on air horn casting —
aligning hole in pump lever with hole in horn casting .
Using screwdriver, push pump lever roll pin back throug h
casting until end of pin is flush with casting bosses i n
air horn (Figure 71).
On other models using the "clipless" rod design ,
connect choke rod into choke lever inside bowl cavity ;
then install upper end of rod into upper choke lever .
Install upper choke lever on end of choke shaft ,
aligning slots in lever with slots on end of shaft, an d
install attaching screw. Tighten screw securely. If an air
valve lockout lever is used, make sure tang on uppe r
choke lever is located beneath tang on air valve lock out lever before tightening screw.
NOTICE : Make sure that the flats on the end
of the choke shaft align with the slot in the
choke lever .
6. If used, install idle vent valve on locating pins afte r
engaging with actuating wire . Install attaching scre w
and tighten securely .
NOTICE: Some models use a thermostaticall y
controlled idle vent valve . On these, install
the thermostatic bi-metal strip first, the n
the spring arm on top to the bi-metal strip .
Then install attaching screw . Install dust
cover under air horn screw.
7. On models using a vacuum operated vent switch
valve, carefully install diaphragm and stem in diaphrag m
retainer; then install diaphragm and retainer in air horn,
Figure 71 Installing Pump Leve r
NOTICE : Use care installing the small rol l
pin to prevent damage to pump lever casting
bosses .
NOTICE : If the "clipless" pump rod design
9D•5
March 198 1
Page 42
'
F
Delco
is not used, install pump rod in pump leve r
and retain with clip .
NOTICE: The front vacuum break, rea r
vacuum break (if used), and fast idle ca m
(choke rod) adjustments must be performed ,
and the thermostatic coil lever inside th e
choke housing has be be indexed properl y
before installing the choke thermostatic coi l
and cover assembly, and gasket (if used) .
Refer to the adjustment procedures and specifications contained in Section "D" of th e
Delco Carburetor Parts and Service Manua l
(9X) .
10. After the vacuum break(s), fast idle cam, an d
inside thermostatic coil lever are adjusted, install fron t
and rear (if used) vacuum break hoses . Then, th e
thermostatic coil and cover assembly, and gasket (i f
used), should be installed and the cover assembl y
rotated until the choke valve just closes . At this point ,
the index cover should be adjusted . Install three choke
cover retainers, and screws where used, and tighte n
securely.
On late model carburetors where tamper resistant
rivets and retainers were removed during disassembly ,
(and after the inside coil lever, fast idle cam, chok e
rod, and front and rear vacuum break adjustments
have been checked), install the cover and coil assembl y
in choke housing by following the instructions supplie d
in new choke cover retaining kit .
NOTICE: On M4ME models, ground contac t
for the electric choke is provided by a metal
plate located at the rear of the choke assembly. DO NOT INSTALL A CHOKE COVE R
GASKET BETWEEN THE ELECTRI C
CHOKE ASSEMBLY AND THE CHOKE
HOUSING .
11. If the C.E.C . valve or idle stop solenoid was
removed from the bracket for replacement purposes ,
install solenoid in bracket, lockwasher, and retaining
nut. Tighten nut securely, making sure lockwasher tab s
align with slots in bracket and flats on hex portion o f
solenoid nut . Then, bend back tabs to retain the nut .
If mounting bracket was removed from the air horn
for replacement purposes, install solenoid and bracke t
assembly on locating lugs on air horn . Then, install
screw securing solenoid bracket to float bowl . Tighten
screw securely . Then crimp bracket tabs on air horn .
Install vacuum hose from tube on float bowl to C .E .C.
valve .
12. On other models, install (2) screws in bracket to
retain the idle speed solenoid, A/C idle speed solenoid ,
throttle closing dashpot, or throttle lever actuator to the
float bowl . Tighten screws securely.
NOTICE: Whenever a service replacemen t
throttle body is installed on 4MV-4M C
models equipped for exhaust emission control
(except 4MV Pontiac), the following adjustment procedures must be performed carefully :
a. With carburetor assembled, place a .300" plu g
gauge or drill in forward vent tube in air horn . Wit h
slight downward pressure on plug gauge or drill, seat
power piston .
b. Using screwdriver, back APT screw in throttl e
body OUT until power piston is completely seated.
c. From this position, turn APT screw inward unti l
power piston starts to move upward .
d. From this point, turn APT screw in the specified number of turns listed on the instruction shee t
included in the service replacement throttle body pack age.
e. After adjustment, remove plug gauge or dril l
from air horn and install welch plug (furnished wit h
throttle body) over APT screw .
ADJUSTMENT PROCEDURES AN D
SPECIFICATION S
Refer to the Delco Carburetor 9X Manual "C" Sectio n
for Replacement Parts and "D" Section for Trouble
Shooting, Adjustment Procedures and Specifications ,
for each carburetor model . The adjustments should b e
performed in sequence listed as applicable to eac h
carburetor model .
The 9X Manual, Carburetor Tools and Gages, ar e
available through AC-Delco suppliers .
9D- 5
March 198 1
Page 43
TYPICAL EXPLODED VIEW — QUADRAJET
PART S
10
6
7
8
4
10
51
14
49
53
58
16A
233
41
35
-
25
29
31
a ii t
y 1,'~
1
30
20
43
9 5
9I
P.' 5 6
\I
~~``
20
28
/
01
48
55
,pa \
02
50
36
33
12
2
15
I 19
42
`9 1
_
68
52
40
66
J JJ
38
`
i.) [
: IIII I.L I ►o
lbs .'.
;; ~—!
w--t-'
_
~4'V
i
54
00
`` 69
~/
/
.//
i y `~
II
•
h
*~ 65
63
~~
Y6
24
22
21
04
34
v -
1,
ELECTRIC
CHOKE MODELS
81
C&
-
09
r
08
80
08
60
62 61
60
~i
±—
/
°
00
Air Horn Parts
Air Horn Assembly
Gasket-Air Horn to FI B
Lever-Pump Actuating
Roll Pin-Pump Lever Hinge
Screw-Air Horn to T/B (Long)
Screw-Air Horn to F/B (Short )
Screw-Air Horn to F/B Countersunk )
Metering Rod-Secondary
Holder and Screw-Secondary Metering Rod
Baffle-Air Hor n
Seal-Pump Stem
Retainer-Pump Stem Seal
Choke Part s
13
Vacuum Break Cont & Brkt Asm (Prim )
14
Screw-Vacuum Break Attachin g
15
Hose-Vacuum Break
Link-Air Valv e
16
16A Link-Air Valve (Truck)
10
Lever-Choke (Upper)
18
Screw-Choke Lever Atch
19
Link-Choke
20
Lever-Inter Choke Shaft (lower )
21
Seal-Inter Choke Shaft (Hot Air Choke)
22
Lever-Secondary Throttle Lockout
Link-Rear Vacuum Break
23
24
Inter Choke Shaft & Lever Mm
25
Cam-Fast Idl e
26
Seal-Choke Hag to F/B (Hot Air Choke)
20
Choke Housing Asm .
28
Screw-Choke Housing to FIB tch
29
Seal-Inter Choke Shaft (Hot Air Choke)
30
Lever-Choke Coi l
31
Screw-Choke Coil Lever
32
Gasket-Stet Cover (Hot Air Choke )
33
Choke Cover & Coil Asm (Hot Air Choke )
34
Choke Cover &Coil Asm (Electric Choke)
35
Kit-Stat Cover Attachin g
36
Rear Vacuum Break Cont & Brkt Asm/Secd
30
Screw-Vacuum Break Cont Attaching
Float Yawl Parts
38
Float Bowl Assembl y
39
Primary Metering Jet As m
40
Ball-Pump Discharge
41
Retainer-Pump Discharge Bal l
42
Baffle-Pump Wel l
43
Needle &Seat Assembl y
44
Float & Lever Assembl y
45
Hinge Pin-Float Assembly
46
Power Piston Assembl y
40
Spring-Power Pisto n
48
Rod-Primary Meterin g
49
Spring-Metering Rod Retaine r
50
1
2
3
4
5
6
0
8
9
10
11
12
06
;•
'---
03
_
~l
53
54
55
56
50
58
59
60
61
62
63
64
65
66
60
68
69
00
01
02
03
04
05
06
00
08
09
80
81
Figure 72 Typical Quadrajet Assembl y
Ei
p Return
Pump Plunger Assembly
Link-Pump Plunger
Baffle-Secondary Bores
Idle Compensator Assembly
Seal-Idle Compensator
Cover-Idle Compensato r
Screw-ldle Compensator Cover
Filter r Nut-Fuel Inle t
Gasket-Filter Nu t
Filter-Filter Inle t
Spring-Fuel Filter
Screw-Throttle Sto p
Spring-Throttle Stop Scre w
Idle Solenoid & Bracket Assembl y
Idle Load Compensator & Bracket Assembl y
Bracket-Throttle Return Sprin g
Actuator-Throttle Lever (Truck Only )
Bracket-Throttle Lever Actuator (Truck Only )
Washer-Actuator Nut (Truck Only)
Nut-Actuator Attaching (Truck Only )
Screw-Bracket Attaching
Throttle Body Parts
Throttle Body Assembly
Gasket-Throttle Body to F/B
Screw-Throttle Body to F/ B
Idle Needle & Spring Assembl y
Screw-Fast Idle Adjusting
Spring-Fast Idle Scre w
Tee-Vacuum Hose
Gasket-Insulator Flange
0
u t Carburetor
Models 4MV-4MC-M4ME-M4M C
Service Manual
GM
Delco
Delco Carburetor
'
F
BULLETIN : 9C-4000
DATE : NOVEMBER, 197 5
PAGE : 1
REPLACES 9C-400 0
DATED JANUARY 197 5
MODEL 4MC GUADRAJE T
1973-76 GMC MOTOR HOM E
Delco
455 CUBIC INCH OLDS ENGIN E
PARTS SHOWN ARE FOR IDENTIFICATION ONLY . CONSULT PARTS LIST FOR CORRECT PART NAME AND NUMBE R
14
eZ-' AID
l'M.TIi~~0 _
0n
v r~U/
_
~~~
3
8
2l
AIR HORN PARTS
g
II
6 7
10
~ 9*
58
41
=t.
6
40
tf)
c5
57
i
27
FLOAT BOWL PARTS
es
69
29
3~
1
3g'J
64
~~p
36 43
34.
*PI)
0
66
71%
7N
165
37
56
45
33
50
25
CHOKE PART S
~ltlr~
52
~~ro •~
24 _-22
,
59.
A
53
IN
17
15
16
13
12
®19
2
o
22 ~20
21
2
.0 30
9
~2"'
55 54,
cam,
r3
~~ ►
_
61
67`
~~
72
60
THROTTLE BODY PART S
PARTS IN ALL COLUMNS SAME — EXCEPT WHERE INDICATE D
1975-7 6
1973-74
7043254
24-404
7046812
9258
40-419
Illus . No .
1
2
3
4
5
6
7
8
9
10
—
—
7047976
7029087
7048169
9428787
7029912
7014699
7031105
7045780
7034522
7037968
7035344
7030753
CO, WD, 131, 1J2 :16, 9X, 9FR, 9FD
FED
7045254
24-405
17051886
9269
40-428
CALIF .
7045554
24-406
17051886
9269
40-428
AIR HORN PART S
7047976
17051386
_
APPLICATIO N
CARBURETOR No .
REPLACEMENT PACKAGE No .
OVERHAUL KI T
POWER CARBURETOR KIT
GASKET SE T
Air Horn Assembl y
Gasket—Air Horn
Lever-Pump Actuatin g
Roll Pin—Pump & Lockout Lever Hing e
Screw—Air Hor n
Screw—Air Hor n
Screw—Air Hor n
Metering Rod—Secondary
Sec . Metering Rod Holder Ki t
Lever—Air Valve Lockou t
Air Valve Spring & Cam Kit
Air Valve Stop
PRINTED IN U .S .A .
©1975 GENERAL MOTORS CORP .
BULLETIN : 9C-4000
PAGE : 2
l
Illus . No.
11
12
13
14
I
7045254
7036881
7002760
7047499
7045554
77050961
1705096 1
---
.__ _ _ .v-
7038305
_
7038581
__._. . - _
703519.9
7026339
7038259
70453555
7029866
21
22
23
7038269
7036880
25
Rod-Choke
le Housing Assembl y
inlet Choke.
ft&!,,everSea :~-Inter. hake S Taft
- 7038282
7037569
7030662
7038285
-
26
27
28
29
30
r
r
-.7043367 : ..
31
32
7011271
=111111MIE
Erin MM.
~~„
LOA BOWL PART S
33
7046757
34
7031970
•
35
7002117
36
-7029849 ' -;
37 _ ~__- - 30 142
38
KI T JNLY
r1 : ~iy'
_~ _
39
7033731
I'
?03;T~
40
41
7'029856
42
7034903
43
7036019
44
7046338 :. :' `
45
46
47
7029862
7^45878
7024281
~r t1
7032'Q o
48
!
n
'•
'
61
62
63
64
65
66
67
68
69
70
71
72
7046811
KIT ONLY
Ul
_
=owl
--
-
Screw-Choke Lever
- etain r-Stat Cover
crew-Stet Cover
._
-
imar
.
-
_
• wet Pisto n
od-Primar
• rin•,. eterin • ; ° •-=Primar
_. ter Nut-Fuel Inlet
asket-Filter Nu t
1
:"i . .
i- .
}~
d{M®
rtr~, . 704 ' h~6• . . ?.`
M
w ., .
rew=ldl-S
o~
insert-Fleet - w l
:Baffle-Float'llow l
7041169
. r n-
-urn . Retur n
EE" um • Assemb t
. THROTTLE BODY PARTS
17052803
17051396
7048532
7011479
7038298
7035772
7035998
7035523
7044794
7029900
419047
a
Idle Compensator Assembly
slie `t-Idte Cofinpensato r
_,,,, 3v r--0le Co.r p ensato r Scre
. ~- Art : hin•
.rin •
• . St . • Screw
E
.
7035790
412501
td
s y.
Ball-Putn Disx arse
Retainer
umpDisehar eBal l
-edle & Seat Ass
/Lea ke .
=die Seat
[oat Needle
oat Arse b I
nge Pi
Float Assembl y
,Power Piston Assembl y
z
-
7026138 .
•
~-
5ltrex~r- Goi
y r
., ChokeHs•toBowl
je
r
.s __ _
703136b
7004 ^T_ : '.
7035Q31_
_
_
Rt~'•wl Asset--
rc
51
7003176
700212
7034361
<
3367
SEENEWMEEMEMOME
r:
r:
7n38
7029866
7000614,
Stat Cover, Coil & Gasket Assy .
Gasket-Stat -Cover -
.--Vacuum Break Control & Brkt . Assy .
Vacuum Break Control Assy .
___ _
Rod-Vacuum __
S^rew--Control Attact in g
Cam-Fast Idle ___
Hose-Vacuu m
Choke Snatt
Choke Valve
Screw-Choke Valv e
Lever-lnlermediate-Cboke
7031231
24
52
53
54
55
56
57
58
59
60
CARBURETOR No .
I
7040031
19
20
49
5'0_ _
I
CHOKE PART S
15
16
17
18
_
7043254
419047
Throttle Body Assembly
Gasket-Throttle Bod y
Screw-Throttle Bod y
Idle Needl e
Spring-Idle Needl e
Lever-Cam Followe r
Spring-Cam Leve r
Fast Idle Leve r
Screw-Fast Idle Leve r
Screw-Fast Idle Adjustin g
Spring-Fast Idle Screw
Gasket-Flange
_ _
BULLETIN : 9C-400 1
DATE : NOVEMBER 197 7
PAGE : 1
REPLACES 9C-400 1
DATED NOVEMBER 197 6
Delco Carburetor
MODEL M4MC QUADRAJE T
1977 GMC MOTOR HOM E
403 CUBIC INCH OLDS ENGINE
Delco
n
PARTS SHOWN ARE FOR IDENTIFICATION ONLY . CONSULT PARTS LIST FOR CORRECT PART NAME AND NUMBE R
14
0''',
=.-'a
!11111PL,iboo
.~
1
~~ a4
•ti
—
12
11
T
J
S1;o(
17
}.
l8
S3'
p
O
1
-20 .,. .
•
21
s
_
5
32
29
CHOKE-PARTS
' O--us+n E
_
'3,1
11
23
30
i
AIR HORN PARTS"`
15
13
} S
r
6 7
V
e
?i--
„,t
,
rm
o,
_,
37
6. .
cam .
®~
.
<
_
_ 3aT
h
11
53
4
52
;TAU}
~
I
l'
'
FLOAT BOWL PARTS
Ifi
61
~-
a,
~►
~
~
-
.
. .~
a
~Q~~`
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48
i
4
far, .
1111)
}_ .
49 M
`~ 4 1 . , 3
THROTTLE BODY PART S
PARTS IN ALL COLUMNS SAME — EXCEPT WHERE INDICATE D
FE0 A _-w _
CALIFORNIA
17057154'- `:~ :J -- - -17057.559
APPLICATIO N
k ;. : -CARB U RETIR RJllo _ '
-REPLACEMENT
No .
170
17055023
-OVERHAUL . FT
A.
._
9319
4319:7R KI T
NER CAR UR
ao-asa __
40-454
GASKET SET-- , rt.
Illus . No .
71" : e , N;PARTS
r: F
1
17055497
17055'919 +
f''Pit1-Horn Assembl y
2
.17051797
Gaskiet-Air Horn
Lever-Pump Actuating
3
7048169
4
9428787
Roll Pin—Pump & Lockout Lever Hing e
5
7029912
Screw—Air Hor n
7014699
Screw—Air Hor n
6
7
7031105
Screw—Air Hor n
Metering Rod—Secondary
8
7045780
7034522
Sec . Metering Rod Holder Ki t
9
10
—
—
Lever—Air Valve Lockou t
—
Air Valve Spring & Cam Ki t
7035344
—
—
—
Air Valve Stop
PRINTED IN U .S .A.
CO, WD, 131, 132 :M, 9X, 9FD
© 1977 GENERAL MOTORS CORP .
BULLETIN: 9C400 1
PAGE : 2
Illus. No.
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25 _
26
27
28
29
30—
31
32
36 •-
_
—
_
57
58_
59
60
61
62
63
64
65
66
67
68
69
70
71
72
y
7031231
70411;472
17055095
7041492
r7O375 .
==:
r .
..._
'70 4 3 . .
o°
• :6
.00614
;=~ 701- 270
. =
1:70554 . 8
7031975
7 0 ®2117
~9 o.
`
...
? .. . . ~•
LPARTS
"
'1705592V
: <,
o
'i
.;
a `. x
M2
~~.
0" •
o
955
o-
. .-
Stat Cover, Coil & Gasket Assy .
Gasket-Stat Cover , -.
Vacuum Break Control & Bracket Alp .
Vacu,l m iireaic Control Assy.
Rod-Vacuu m
Screw-Control Attachin g
Cam-Fast Idl e
Hose-Vacuum
Choke Shaft
Choke Valv e
Screw-Choke Valv e
Lever-I ntermediat-e`Chbke
Rod-;Chok e
Choke Sousing Assembl y
-1nterme late-Gh . ,- Shaft & Waver Ass
-Seal-1
'mediate ho eS aft
- Seal= . _,
,Zsl:`
'crew--- •il -ever S
-Screw hdke Hs . . to Bowl -' pro : .
r. -
a
rew-Choke Leve r
Ret-iner tat Cove r
' Scr -S at Cover
Flo : B•'`°` Assembl
' Jet ri
Ball-Pum • Disch
; etainer-P ' • iiischar .e Bo
.. .Nee . & Seat Ass . .
Gasket-N die Sea t
"oat Needl e
loot . ssemb l
Hinge•Pin-Float Assembl y
Power Piston Assernbl
otraet Pisto n
-taw St.
-~~.Ro'd=-Prima r
r $Frog- ele:ring Ro•rimary--.;
Nut-Fuel Inle t
:.. asket-Filter
Nut
-. t . ,
i _
"
5•
,
- ,,,
b
le
49
50
51
.
53
54
55
56
17056632
70
- -
41
42
43
44
45
46
47
4&
CARBURETOR No.
7029 :6 .
0
34
—
_•
17054309
17050961
7044435
:,•, ; . ,.
7041527
17050732
17Q566 91
7 339
7038259
704890.4 _
17057559
i
CHOKE PAR T
704336 :
—
_ 38
- -'9
17057254
_
NiFniff'"' sa
-.
00
ea
ov
Qv:
= d ° C.
ldle-Comt52
,
'o`r
n ator
rew-Cover Attadlilnlgk
At i
Sprin -Idle Stti S
($
nt
o.
- crew-Idle tay --_,
70' 14, .1' =
inser
oat-Bowl
:703 :1
- '.'
s
--_
prr
um p. Retur n
170530721 - = =. ifigarnalOUMMIM
Pum• Assembly '
7026138
ott ' 13
-70, . 0 :_; . . ( UNIMMUMMMEEM)
Insert-Aneroid vit
, :'
7041473' x:
Lever-Secondary Lockou t
THROTTLE ~Bfll'3Y PARTS
_L1_170.8_885'
1 57054744
Throttle Body Assethb`ly
KIT ONLY
Gasket-Throttle Bod y
7035790
Screw-Throttle Bod y
7048532
Idle Needl e
7011479
Spring-Idle Needl e
7041497
Lever-Cam Followe r
17051494
Spring-Cam Leve r
7041498
_
Fast Idle Lever
7036079
Screw-Fast Idle Lever
7044794
Screw-Fast Idle Adjustin g
7029900
Spring-Fast Idle Scre w
419047
Gasket-Flange
,
,
._
BULLETIN : 9C-400 2
DATE : NOVEMBER 197 7
PAGE : 1
De1co Carburetor
MODEL M4MC QUADRAJE T
1978 GMC MOTOR HOM E
403 CUBIC INCH OLDS ENGIN E
PARTSSHOWN ARE FORIDENTIFICATIONONLYcCONSULT PARTS LIST FORCORRECT'PAR*AME AND NUMBE R
14
rI;-is
.-rA.
15
._
16
,
II
5l~ V
r";
--
.- ;orl
' 02=11219
_
'
9i'f'
-
"_
19 J
f OH
)'
,86 )
4=
'r
I
AIR ...HORN_MR TS
4#44)f(E#Afitt.s _ .
j 4
00 ,'s- erO V
6( ,t g.q L_ _
-
113
,Mlp*^
1110
r804
f
a c -^1--.--
:•
JQ
,R
:t_
rAl .
9R .
19VI)
1„„--
23
22
f
0 .13
9
- 044:
.
'
4111&\
0110 '
B8 -07
4-7-19AIS1 9
'' = 9
"cz) ,,,
I.,,.
D9
R4,
47oft 1
+
n.1,f)
, i---i'q
tit-i
..
;
49
FLOAT IIOVIL FnAt4tt _20! 127 1, 12!
PARTS IN ALL COLUMNS SAME —EXCEPT WHERE INDICATE D
_.
..____. __
-
_ ___
MMOMiralhn ''
1511559._
J
=,.
_rt.
_
1St
&E-No i
=I=
MAUL-
-- -
=11111111111F.'
--t- '
-'W.CTIETT,t-' KITMijiMMIMMM
. 3'coF.ao ,
Iles . o .
At. . . .
''WIM11111111111MMI1111111EMEE.11IN
a
o
AM1081MISPH1111*1111IMMIll Vilf1lixv Uer Mr
O. •
.,
ir cittkr
..
7048169
a, sit .' evor F-ParIvIsictntati
4
9428787 ybo i
Roll Pin-PumWkUtII(lout
Levet Hinge , a
_
5
7029912 t . .
Screwi-Air HotnIf,C1
6
7014699
Screw-Air Hofri
-7
7031105
Screw-Air Horn
8
7045780
Metering Rod-Seconda r
9
7034522
Sec . Metering Rod Holder Ki t
10
Lever-Air Valve Lockou t
7035344
Air Valve Spring & Cam Ki t
Air Valve Stop
CO, WD, 131, 132 :M, 9X, 9FD
PRINTED IN U .S .A.
© 1977 GENERAL MOTORS CORP .
BULLETIN : 9C400 2
PAGE : 2
17058254
Illus . No .
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
—
—
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
—
—
61
62
63
64
65
66
67
68
69
70
71
72
I
CARBURETOR No .
17058559
CHOKE PARTS
17054309
17050961
7044435
—
—
7041527
17050732
17056631
17056632
7026339
7038259
7048904
7029866
7031231
7041472
17055613
17065040
17050754
7037569
7043367
_
7043368
7019709
7038808
7041542
7029866
7000614
7011270
FLOAT 3OWL PARTS
17055633
17065039
7031978
7031974
7002117
7029849
30-134
KIT ONLY
7033751
7046300
7041469
7044449
7036019
17055329
17056953
17051353
7041459
_
17059861
7024281
GF-441
7032732
—
—
—
—
7003176
7002121
7041471
7031365
7042979
17053072
7026138
17051796
7041473
THROTTLE BODY PART S
17058648
17058984
KIT ONLY
_
7035790
7048532
7011479
7041497
17051494
7041498
7036079
7044794
7029900
419047
Stat Cover, Coil & Gasket Assy .
Gasket—Stat Cove r
Vacuum Break Control & Bracket Assy .
Vacuum Break Control Assy .
Rod-Vacuu m
Screw—Control Attachin g
Cam—Fast Idle
Hose—Vacuu m
Choke Shaf
t
Choke Valve
Screw—Choke Valve
Lever—Intermediate Choke
Rod—Choke
Choke Housing Assembl y
Intermediate Choke Shaft & Lever Assy .
Seal—Intermediate Choke Shaft
Seal—Choke Hsg . to Bowl
Lever—Stat Coi l
Screw—Coil Lever
Screw—Choke Hsg . to Bowl
Lever—Chok e
Screw—Choke Leve r
Retainer—Stat Cove r
Screw—Stat Cove r
_
Float Bowl Assembl y
Jet—Primary
Ball—Pump Discharge
Retainer—Pump Discharge Bal l
Needle & Seat Assy .
Gasket—Needle Sea t
Pull Clip—Float Needl e
Float Assembl y
Hinge Pin Float Assembl y
Power Piston Assembl y
Spring—Power Pisto n
Metering Rod—Primary
Spring-Metering Rod—Primary
Filter Nut—Fuel Inle t
Gasket—Filter Nut
Filter—Fuel Inlet
Spring Fuel Filter
Idle Compensator Assembly
Gasket—Idle Compensator
Cover—Idle Compensator
Screw—Cover Attachin g
Spring—Idle Stop Scre w
Screw—Idle Stop
Insert—Float Bow l
Baffle-Float Bow l
Spring—Pump Return
Pump Assembl y
Rod—Pum p
Insert—Aneroid Cavit y
Lever—Secondary Lockou t
Throttle Body Assembly
Gasket—Throttle Bod y
Screw—Throttle Bod y
Idle Needl e
Spring—Idle Needl e
Lever—Cam Followe r
Spring—Cam Leve r
Fast Idle Leve r
Screw—Fast Idle Leve r
Screw—Fast Idle Adjustin g
Spring—Fast Idle Scre w
Gasket—Flange
_